The Gigabyte X1950 Pro is one of the highest clocked cards.
The HIS X1950 Pro is the king of the hill in std clock speeds.
The PowerColor is clocked at 600core clock speed.
The Sapphire is clocked at 580 core ane 1400 memory.
The ATI is the lowest of all in clock speeds.
The HIS X1950 Pro is clocked higher than the review sites could take any of the other 1950 Pro cards.
These cards do not OC well. I read a lot of reviews and the memory on these cards are set to max at about 1400.
The core on any does not go higher than 621 if you are lucky enough to get a good card.
It is I think the chip next to the power connection, I would put a ramsink on whatever does not have one on the back though to keep it cool. This is why I think the HIS got a lot higher is due to it covers the whole PCB.