HIS and Sapphire Radeon HD 4850 Face Off

Overclocking either of the HIS or Sapphire Radeon HD 4850 cards may seem easy; just go into the ATI Catalyst Control Center and click on the Overdrive tab, right?  Well, not so fast.  Perhaps this might work on default clocked cards, but with caps set at 700 MHz for the GPU and 1200 MHz for the memory, that doesn't leave much room to work with.  Instead, we turned to the AMD GPU Overclocking Tool which let us set whatever clock speeds they want. 

Starting with HIS first, we raised the core and memory speeds about 5 MHz at a time until we found any sort of instability or artifacting.  This resulted in a long process of raising speeds, testing, noting the results and then raising speeds once again until finally, at 780MHz on the core and 1195 on the memory we got a black screen and Vista crashed hard.  Getting back into Windows, we continued backtracking from there until we finally arrived back at 775 MHz on the GPU, and then went back to the memory overclocking.  It appears that we didn't have much further to go, as anything over 1200 MHz caused artifacts to appear when running 3DMark06.  Final results for the HIS were 775 MHz GPU and 1200 MHz memory - a 90 MHz bump for the core while gaining 100 MHz on the memory.

Next up was Sapphire's Toxic card.  With a goal in mind, we quickly raised speeds to just under the results we got with HIS and then moved up more slowly after that.  We were only able to go about three rounds of raising speeds before hit our first snag.  Once we hit 760 MHz on the core, we would repeatedly get device driver crashes launching any of the benchmark applications.  Lowering this speed by a few MHz got us a stable system.  The memory, which was already 50 MHz faster than HIS' card to start with also sputtered out early as we were only able to gain an additional 16 MHz there before running into issues.  Our results with Sapphire's card were 756 MHz / 1166 MHz, well under what we achieved with the HIS version.  Looks like the IceQ4 cooler has earned its merits.

FINAL OVERCLOCKING RESULTS

With our overclocked cards running stable, we decided to give 3DMark Vantage another run-through to see what kind of frame rate increases we might be looking at.

Each card saw nearly a 25% increase in GPU speed and 15% on the memory over the default clock speeds of the Radeon HD 4850 (625 / 993).  As shown in the 3DMark Vantage GPU tests, that resulted in large increases in the first test's frame rates, with a more modest bump in the second test.  Overall, the results of overclocking the cards were quite favorable, giving us performance that was close to but not quite that of the pricier HD 4870.