Adobe, ColdFusion ,Flex, ColdFusion 8 ,Flex 3

That totally depends on your application and how it was done, the size of the database, how the databse is built and indexed... A specific count is almost impossible to give with any sort of accuracy just based on the spec. However, I don't think you need to worry about when to switch to CF8 Ent. I think when the time comes your focus would be more on getting additional hardware.
Your application should be done in a way to support adding additional servers and hardware as needed.
Harel

yagamami is correct, it's far more about how your code and db are set up

enterprise will give you more options like multiple server instances(clustering), sandboxing and monitoring.

but not likely more users per box... clustering will allow you to expand to multiple machines but the volume they handle per machine should be the same.

one thing it does provide is connectors to enterprise class db's (DB2, Oracle,k Sysbase etc) so your properly written app will benefit from the speed and features of those tools.

Hmm, doesn't CF 8 Standard have a limit on the number of threads is allows; whereas, CF8 Enterprise has no cap?

I'm not sure about the thread limits, but from experience I can tell you that relying on JRun's clustering capabilities should be done at your peril.  Also keep in mind that Jrun is a dead product which is about to reach its end of life, and that last I checked jboss had coldfusion clustering issues.

I found that actually using the lo-tech client variables approach and keeping session state to a minimum as well as making sessions be able to recreate their state if need be, can give you instant out the box super clustering without the overhead of j2ee clustering.
I am running a very large app with a large user base and I can bring servers up and down on a whim, without using session state or user data. Use client variable and keep the client data on a separate database. Have all servers use that database to maintain session states.

Harel
 

Interesting. That is sort of like my thinking ( i think??) .  If i load up my box with lots of RAM, leverage the caching of the DBMS and utilize stored procs then  CF8 becomes merely a gateway for queries, i thought i could probably serve about 40 to 75 concurrent users quite easily . For me, its as much a question of economics. The reason i want to use CF8 is the fact that it is so easy and quick to code. I'm putting a lot of emphasis on how to simplify code maintenance and have not found any other app server that competes with CF in that area. I'm fairly experienced with developing and implementing web apps on Java servers (primarily Websphere + Oracle) but for this project I can't afford those for the reasons above. (simplicity, maintenance and cost).
I was hoping for comments from people that have done some profiling / load testing on similarconfigs.

i'm going to close this out. thanks for your comments. i'm thinking i needed to word the question more precisely. its my first on the trial subscription (1 week)