Memory rated at 2-3-3-6, but Bios shows 2.5-4-4-8. Mobo=Intel D915GAG. Is speed diff a problem?

Gentlemen,

I've purchased a pair of PQI DDR400 memory sticks, rated at 2-3-3-6.  This memory was selected because it was faster than most other memory, and still in the reasonable price range.

After installing the memory sticks, the Bios shows the memory as being 2.5-4-4-8.  

In the Bios, under Advanced -> ChipSet Configuration -> Memory, there are some memory adjustments that can be made.  
SDRAM Timing Control = Manual [Auto, Manual-Aggressive]
CPC Override = Enabled [Disabled]
SDRAM frequence = 400Mhz [266, 333, 533, 667]
SDRAM tCL = 2.0 [1.5, 2.5, 3.0]
tRCD = 3 [2, 4, 5]
SDRAM tCP = 3 [2, 4, 5]
SDRAM tRASmin = 6 [3, 4, 5, 7, 8, 9, 10,11,12,13,14,15]

Total Memory = 512MB
Memory Mode = Dual Channel
Memory Channel A
  Slot 0: 256 MB SPD: 2.5-4-4-8
  Slot 1: not installed
Memory Channel B
  Slot 0: 256 MB SPD: 2.5.4.4.8

Note: SPD defined as tCL-tRCD-tRP-tRASmin

I'm interested that, even though I've explicitely defined the memory speeds, the mobo seems to have evaluated the memory timings and overrode my settings.  If the memory would not be stable at a faster speed, I can appreciate a safety override.  However, I bought what I thought was faster memory.

My questions:

Is the memory actually slower, or am I giving the mobo too much credit for intelligence and not expressing the memory speed correctly?

Is this speed difference practically measureble, and a significant and noticeable difference in application amd computational performance that I should be concerned?