Elite Bastards published a review on the Sapphire Radeon HD 2600 XT 256MB GDDR3 video card

The core clock speed of Sapphire's GDD3 and GDDR4 Radeon HD 2600 XT offerings are identical, only the memory clock (and of course type) is different, with the GDDR3 board finds itself with RAM clocked some 400MHz slower than its big brother. However, there are also some rather large visual changes between the two boards.

Physically, the GDDR3 Radeon HD 2600 XT looks very different to its GDDR4 cousin - The PCB is much shorter for starters, and gone is the long reference cooler, replaced with a much smaller (yet still single slot offering). Once more, no external power is required, and this board also fully supports CrossFire via the two bridge connectors needed to get an ATI multi-GPU rig up and running.

Sapphire Radeon HD 2600 XT 256MB GDDR3 Review