i have oc'd my cpu to 3 ghz and will have another go with 3dmark and see if it helps. if all goes well then possible and cheap solution would be to buy a better cpu cooler to withstand better overclocks.
thats a fairly low score. i used to get 12900 with my q6600 @ 3.0ghz + stock 4850 (after the silly 8.12 upgrade it went down to 11800, that and some bsods started to happen). but i think you should beat/match a 4870 which should probably fall around 14k.
its mainly from your cpu bottleneck, im pretty sure it can go way over 16k just like TB303 has his system, I got a 16150 on 3DMark 2006 and my system specs are:
Intel Core 2 Quad Q6600 (400x9 3.6Ghz - 1.46Vcore) i got the GO revision but HIGH VID
Cooler Master Hyper 212 cooler
2GB Patriot LLK DDR2 PC6400
EVGA 8800 GTS G92 512mb OC to 800core/2000shader/2160memory
Asus P5N-D 750i SLI
Cooler Master 650w extreme power
Antec P182 case
i wish i had the same cpu as TB303 otherwise my Q6600 would have run cooler damn VID. but yea your main issue is the CPU that is way bottlenecking ur powerful GPU
so if i get it right i naturally get lower score with gtx 260 and e6750 because cpu score wont get so high as with quadcore. then i suppose that most games that dont support quadcore my gtx 260 wont be slown down by my cpu. for example cod4.
Run a game benchmark, I know FarCry2 has a benchmark built into it. That is what will really matter. A few years ago My buddy had(still has it) a dual dual core Opteron (2 CPU's 2 cores each) with 8GB of ram, running Xp 64 bit, on a Tyan motherboard with a 7950GX2. At the time I had the system I have now but with an ATI x1900XTX OCed to all hell. He roasted me on 3dMark05 and every synthetic benchmark known to man. But when we played and ran game benches. I kept up or even toasted him in some. 3Dmark is good for an overall comparison, but really when it comes down to it your game performance is what matters, or whatever software you are running.
You can't compare your scores with quad cores simply for the fact 3dMark06 loves to utilize as many cores as you can throw at it.
I have an "old" EVGA 8800 GTS 512 and got 15,202 with an e8400 OC'd to 3.99 GHz (9 X 444 FSB) but I had to even OC the GPU to get that score and set my NVidia Control Panel to performance preference.
On GPU stock speeds and stock e8400 I "only" get around 12,700.
Your bottleneck is your FSB. When you see the really high scores in the Futuremark ORB for single card scores you'll find most of those to be in 470 and up FSB speeds.