The 2600 Pro card I'm looking at today is actually made by Sapphire and comes slightly overclocked to 700MHz/700MHz. Physically, the card is identical to ATI's reference design though. To differentiate itself the card's PCB and cooler shroud have been coloured blue and a Sapphire sticker sits in the middle of the fan.
While the 2600 XT was a surprisingly large card, the Pro version is a much more respectable size, which further suggests later XT variants will become smaller. Also, as the RAM runs at a slower speed it doesn't need to be actively cooled so the heatsink on the Pro cooler only covers the actual GPU core, further reducing the card's weight.
The cooler itself is just a mini version of the one on the 2600 XT and noise output is along the same lines.
In every other aspect the 2600 Pro is the exact same is its bigger brother with no extra power needed, the same CrossFire connectors used, and, the same output configurations on offer.