Overclocking

With claims from ATI that the HD 4890 GPU can overclock to 1GHz and beyond, we were clearly intrigued as to what speed we could coax from our Asus card. RivaTuner didn't know what a HD 4890 was, so we resorted to the OverDrive tool in the Catalyst driver.

Alas, 1GHz was too much to ask with the GPU finally topping out at 965MHz. This isn't a bad effort from the 850MHz stock speed, but a bit disappointing given the expectations created by ATI's marketing hype. The GDDR5 memory was happy to run at 1,100MHz (4.4GHz effective) which also isn't bad from a stock speed of 975MHz (3.9GHz effective).

Meanwhile, Nvidia hadn't made many claims at all about the overclockability of the GTX 275 - an hour and a half-long briefing call on the GTX 275 mentioned the new card for roughly five minutes before moving onto bore us about PhysX and CUDA applications. Yes, PhysX and CUDA are interesting, but come on Nvidia. With no expectations set in pre-testing briefings, we set about overclocking the GTX 275 in fairly modest increments.

Which was a huge waste of time, as our GTX 275 was massively overclockable. We pushed the core speed from 633MHz all the way 745MHz while the stream processors were happy to run at 1,652MHz - a huge leap from 1,404MHz. Finally the GDDR3 memory of the card could be pushed to1,295MHz (2,590MHz effective) up from the standard 2,268MHz.

The following graph shows how much these overclocks affected Crysis performance.



Even with the big overclock, the HD 4890 struggles to match the stock-speed performance of the GTX 275 at 1,680 x 1,050 with 4x AA. The overclock from the GTX 275 is incredibly helpful meanwhile, boosting the minimum from 23fps to a much smoother 27fps.

At 1,920 x 1,200 with 2x AA, the HD 4890 does surpass the performance of the GTX 275 at stock speeds, but only just with its average of 34.1fps compared to 32.1fps. The overclocked GTX 275 can just about manage Crysis at 1,920 x 1,200 with 2x AA with a minimum of 23fps.