Just ran two 3dMark Vantage benchmark tests, one with my single GTX 470 with stock speeds and the other test with card OC'd 850/170/1800 @ 1.050 volts (increased from .937v).
Here were the results: (Click on image twice to see full-size picture)
As you can see, that's nearly a 6000 point difference between the two, with a simple OC. Also, temps never passed 76C, well under the GPU's thermal limit. If anyone else would like to replicate this OC with the same card, I'm also including a picture of the custom fanspeed curve that I utilize, it strikes a nice balance between noise and keeping the card as cool as possible during heavy loads, because as all of us GTX 470 owners know the fan is quite loud and the card runs relatively hot.
I suppose I am posting this because it seems to be common knowledge that the GTX 460 is much more "overclockable" than it's big brother, the GTX 470. This may be so, however to say that the GTX 470 is not overclockable would be definitely incorrect. As my test shows there is plenty of room to OC the card, provided that the voltages are increased accordingly. Without the voltage increased, the card is indeed not able to be OC'd very much.
I've been told that the voltage can safely be increased to approximately ~1.085. at which point I'm sure an even greater stable OC could theoretically be achieved. Anyways, I hope this thread helps someone that's new to OCing with this card.
As a side note, here are the rest of my system specs in case anyone is interested:
CPU - i7 930 2.8 OC'd-4.0Ghz @1.24v
Cooling - Corsair H50
Case - HAF 922
Mobo - RIIE
Video - GTX 470
RAM - Corsiar 6 GB Tri-chan. 1600Mhz
HDD: 500GB 7200RPM RAID0
1TB 7200RPM HDD
1TB eSATA 5700RPM HDD
Optical: Sony BWU-300S BR-Burner
MSi Super-Multi 24x DVD Burner
PSU - Corsair HX850
Just FYI, your CPU score is very out of whack, the reason being CUDA. Vantage is able to use CUDA cores so you get a bloated score... to get a pure CPU score, just check the "disable PPU" option before running the test. I only have a GT 240, but it bloats my CPU score by almost double.
But yeah, that GPU score is very nice for a single card. You could probably be at 35k with SLI 470s. My 5850s topped out around 30k in CF.