Liquid Cooling?

I recommend Koolance Products... http://www.koolance.com/

 All things considered the 65C is a little higher than normal (Did you measure temp during CPU benchmarks)?  IN any event that temperature is well within normal operating range.   (Be concerned when it is pushing 75C).  The Video card at 70C is well under max temperature.

So first, you are throwing money away if your desire is to get things to run cooler.  You can even slow down fans a little bit and still be well within range, or just look at getting larger fans.  The small ones are the noisy ones.  You can get away with less airflow.

dlethe;
I am more concerned about the increase in ROOM temp than in the machine.  I spend several hours a  day in the loft and it is uncomfortably warm despite my attempts to divert heat.  Essentially, I am wondering if liquid cooling would decrease the overall room temp.  I have exhausted ( no pun intended!) the ventilation options for the space.

No matter what cooling system you use, the same amount of thermal energy is transmitted from the system to the room ==> your system still generates the same amount of heat ... some cooling systems are just more efficient at transferring the heat elsewhere (e.g. your room).

If you're not concerned with the system temps, then switching to a liquid system isn't necessary except as a way to cool it more quietly.   But it won't change the room temperature.

garycase,
thanks for your input.  I understand what you are saying and I suspect that is the case.  My hope was that if I could keep the  system cooler, the room temp would be lower but logically the heat would have to be transferred somewhere.  I am thinking I may want to change my hard drive array to an external unit and the drop the power supply down as much as possible.

there are only a couple options :
put the pc in a box, and drain the warm air outside (with a big tube and fan ?) - or cool the room

Well the whole thing is a bit too much but on the other hand your system i sfully loaded. .At first what is your room temperature.2nd a CPU running at 65C is a lot and i am assuming ur not at full load.Well u have to start one thing at a time.
1st Buy Arctic Silver 5..This is a thermal paste that has good result.
http://www.arcticsilver.com/as5.htm
2nd Take a good look at your Cabling...well i know u have a lot but  again u should try to "hide" them in order to help the airflow.
3rd The HDDs are getting hot because of problematic airflow...Check their position in order to get bettter flow
4th Get a beastier CPU Cooler like this
THERMALTAKE CL-P0310 BIG TYPHOON 120 VX
5th replace the Fans on your Case with motherboard Controlled Fans like these
http://www.arctic-cooling.com/catalog/main.php?cPath=3_48&osCsid=02366e4250f29e67bf3d4dc6142bbaa3 
The Pwm Ones need the 4 Pin Header ....for the other get the 3 pin models and yes NO molex....the MB can Controll your Fans and accordingly to your load adjust their speed.
6th Take a good look where ur system is located.Can u move it to somewhere more convinient....i am talking about the case where is stuck inside a desk and all the tricks of airflow goes useless because it just wont get any air to suck.
Well if this doesn't cover u them its time to get Liquid Cooling...follow the other recommendations.

Also this like a beefy CPU Cooler
http://www.arctic-cooling.com/catalog/product_info.php?cPath=1_43&mID=246

Seems to me you are trying to beat the laws of thermodynamics, and ignoring the real problem.  It is simply too warm in the loft.  Spend a few hundred dollars on a portable air conditioner (if you have a window to exhaust through).  I had similar problem in a home office years ago. Best investment I ever made.  Room temp dropped 10 degrees.  

As I noted above, nothing you do to the system is going to change the temperatures in the room [except turning it off :-)  ].     Simple laws of physics :-)     Nor is your comment "... I am thinking I may want to change my hard drive array to an external unit and the drop the power supply down as much as possible. "  a good idea.    Swapping in a smaller power supply won't make any difference -- any reasonably efficient power supply operating within its range of efficiency (typically 20-85& or rated power) will only draw the actual amount of power that's being used, and a smaller unit would have less "headroom" (extra power available for high-demand periods, such as drive spinups, high CPU utilization, etc.).     If you have an inexpensive, inefficient PSU, then replacing it with a good high efficiency unit (I only use Seasonic and PC Power & Cooling) will reduce the power used and generate less heat, but not enough to make an appreciable difference in the room temperature.

The suggestion above to use a portable A/C unit is probably the simplest way to resolve this, providing you have a useable external vent (window, etc.).    (I presume you've already tried adjusting your current vents)    You may be able to add another vent from your existing system, but that would likely cost as much as a portable unit.

You may also want to test your original assumption -- "... My office is in a loft and the temp is typically 4-5 degrees warmer than the house due to the heat generated from my PC. "      Turn the PC off for a day or so and confirm that the room is indeed 4-5 degrees cooler with it off.    You may be surprised.

Again, thanks to all for the input.  I have compared room temps with the unit on and off and it is definitely the cause.  Incidentally, although I am not an engineer or a physicist, I do have a degree in physics from the University of Illinois (1988).  The issue of thermodynamics is much more complex than is stated here, considering such factors as the efficiency of heat transfer with radiation, convection, or conduction as well as the efficiency of components with given temps etc...   I asked the question so it would be rude of me to argue.  I was hoping to get some input on the pros and cons of liquid cooling, an idea that for whatever reason has not taken off despite being around for a few years.
Certianly, I agree with suggestions that a portable air conditioner vented outside would help and I have a feeling that is going to have to be my solution.  I have one last trick up my sleeve to try first...

A physics degree from Illinois is even better, as it's one of the better schools for physics.    My favorite physics prof had his PhD from Illinois, and I really enjoyed his classes in thermodynamics and quantum mechanics when I did my degrees  [I have undergraduate degrees in math & physics and graduate degrees in math and computer science].    Mine were a few years before 1988, however :-)