In an attempt to spruce up a slightly older machine, I picked up a GTX 550 ti.
 
Core2Duo X6800 (2.93ghz)
4GB 667mhz DDR2
Intel 975x mobo
700W PSU
 
With my old EVGA 8800 GS (moderately overclocked) I had 6.7 for gaming graphics on the Win7 experience index, and 9300 in 3Dmark06.
 
With the new EVGA GTX 550ti I'm only getting a very modest increase... 6.9 for the Windows experience index, and 11000 in 3Dmark06.  Others reported 7.3 or 7.4 experience indexes, and that 3Dmark06 score seems way too low as well.
 
EVGA precision and GPU-Z are reporting all the correct clock speeds, etc.
 
Anybody have any idea what the bottleneck could be?  I'd hate to have to return the card, as it should have been a good price/performance ratio, and just what I was looking for to breathe some affordable life into my setup...  Thanks!

I have an unlocked multiplier.  I already know I can jack it up to 3.2 ghz without raising voltages (3.46 gets dicey).  I can see if that makes an appreciable difference.
 
After I posted I actually ran 3Dmark11 and the few people still using X6800s were in the same vicinity as my score (2268 for combined score).  So maybe this is what is expected...
 
Still though, any other thoughs/opinions?  Thanks!

who cares about windows index as long as your 3dmark score is on par with people with a similar setup to you. are you having framerate problems in game?

^ To clarify, the scores posted above were the "overall" score, not the "combined" score.
 
My GPU score actually dropped from 2377 to 2373 after the CPU overclock (essentially no change).  It was the physics score that got a significant boost after the overclock (2058->2187).
To answer the question above, I don't really "care" about the windows experience index.  I just was disappointed that I was scoring significantly lower than others with the 550 ti.
 
I'm not getting "bad" framerates in games, but the increase I'm seeing over the 8800gs is modest (less than 20% pretty much across the board).  It's noticeable, but disappointing seeing as I just invested in a new card.

Well i just tried 3dMark06 and ive got a Intel Quadcore Q6600 @3.0, 2 gigs of 800mhz ram and the same 550Ti FPB and i hit a 15933 3D Mark score, a mid 6000ish SM2.0 score, a mid 7000 ish SM3.0 score and a 5000 ish CPU score.
 
So its probably a CPU bottleneck you have there.  Heck, even my CPU is bottlenecking this card im pretty sure.
 
My card is overclocked though, i took it to 1022 Core and 2214 memory from the stock 951 core 2078 mem but still.

I may try tonight overclocking via FSB instead of multiplier.  In the past I've messed around with this and found the system to be stable at 1333 (up from 1066) with multiplier set to 10 (3.33ghz).
 
Would locking down my PCI Express Bus be recommended if I do this?  If so what frequency?

prag16

I may try tonight overclocking via FSB instead of multiplier.  In the past I've messed around with this and found the system to be stable at 1333 (up from 1066) with multiplier set to 10 (3.33ghz).

Would locking down my PCI Express Bus be recommended if I do this?  If so what frequency?

 
This is how i overclocked my Q6600 from 2.4 to 3.0, using the 1333 bus up from the stock 1066.  Try to run it oced like this and see if it helps.  It all comes down to mine having the same bus speed with double the cores.
 
Also i don't have 3DMark11, but ill download it and see what i get there tonight or tomarrow, ill post back results when i can

Ok so i downloaded the free version of 3dMark11 and can only use the basic preset of performance, whatever the middle option is to run the bench tests. 
 
I hit a score of 2764 and was considered in the same system range as other setups like mine.  My system specs said i should be hitting 2500 in all things and i was at 2750ish in those things, except it said i should be hitting around 3300 in physics and thats the only area i was under at only 2850ish, weird.
 
Either way i was over the 2500 part of the chart where over 500 other peoples similar setups were and i was in the 2700-2900 section where only about 70 people were so i guess both of our scores are pretty normal, although the chart indicates that mine is a little above average i guess.