I will buy the Sapphire Radeon HD5750 1GB DDR5 VAPOR-X in a week or so, but I am afraid that it will not perform properly (bottleneck) because of my relatively old board. I have an Intel DP35DP board, Q6600 at 2.4GHz and 4GB DDR2 800 MHz with Windows 7 Ultimate 64-bit installed.
Do you think I should buy an older VGA, like the Geforce GTS 250 1GB DDR3, or my system will be able to handle the HD5750??
A 5750 would be good or a 5770 for both dual core and quad core games. You could use a better card for games that take advantage of quad cores and not be bottlenecked but dual core apps would be bottlenecked because of the low clock speed in my opinion.