Weird problems when increasing voltage to my 7850...

Hey guys,

First post here! I built my own PC a few weeks ago, and I've been working out the kinks as I go along. Like the title says, I currently have a 7850, with a stable overclock of 1050/1250 on stock voltage, and +20% on the power slider.

However, if I download ASUS GPU Tweak and increase the voltage to 1.225 V, I can overclock to 1200/1450 with no stability issues at all -- but, whenever I'm playing a game that normally runs well, I'll get very frequent drops from 60 to 40 for roughly a second, and then it'll go back to 60. This happens the most in Team Fortress 2... looking around will drop my FPS to 40 very briefly, which can get very annoying very quickly. The problem persists unless I bring my voltage back to stock and return to my tried-and-true overclock of 1050/1250, which gives me a smooth 60 in TF2, and most games in general.

When I benchmark my GPU at 1050/1250, the scores I get can be a bit low compared to scores I see elsewhere on the internet at similar clock speeds, with a 3DMark graphics score in the 5400s and a Heaven benchmark score in the 1330s (both of which are determined at the 1050/1250 overclock). So, I'm interested in pushing it past that because it seems my card is underperforming from the outset, which makes it sound like it's a bit defective, but I don't have any artifacts or glitches -- just underwhelming performance.

One last question: I'm using the 12.8 Catalyst drivers. Is that the best one to use? I read all the time that 12.3 is really stable, but, as I'm new to overclocking, I don't see what the benefit is to going back to an older driver when newer ones seem to promise game-specific performance increases.

Anyway, to sum up: Increasing voltage and clock speeds gives me higher benchmark scores and max framerates, but worse performance.

Here's my entire build:

i5-2500k at stock speeds
500W Corsair Builder Series CX500 V2 PSU
8 GB RAM
1 TB 5400 rpm HD (I know it's slow, but I was on a bit of a budget!)
ASRock Z77 Pro4-M
Radeon HD 7850

Thanks a lot!
Edited by theeraserlol - 8/25/12 at 7:16pm

Under load with those clocks, my card doesn't go above 75C. I'll try to force 3D clocks and see if it helps!

Forcing 3D clocks doesn't get rid of the stuttering in TF2 so far.

One thing I noticed that I think is interesting -- if I leave VSync on like it usually is, the framerate will drop from 60 to 40 for a second, then return. But if I turn VSync off, it'll drop from 220+ to 140ish, then return... a much bigger drop. Temps are normal, clock speeds are constant, GPU load stays at a relatively high amount with little fluctuation, and I've been watching my CPU speeds with CPU-Z to make sure it's not my CPU underclocking and throttling it. I just can't figure out what's causing this problem.

Well, it did.

I was looking through GPU-Z and found that, for some reason, the bus interface was listed as PCI-Express 3.0 x1, instead of x16. So, I moved it over to the next slot -- sure enough, it reads x16 now and everything runs beautifully. Such an easy thing to miss, but now my card is actually behaving like it should!

Thanks for posting in here though; I appreciate it.