X38 is the motherboard chipset. LGA775 is the processor. I wouldn't think any of them will be a huge improvement. The Q6600 is a decent processor. You would see improvement in benchmarks, but you will see more improvements in games putting that money towards a faster video card. Really any processor that is faster will show improvement in synthetic benchmarks, but in real world scenarios will yield little improvement.
I was wondering if upgrading to a faster processor would allow me to use a better GPU such as a Nvidia 260 or ATI 4850 plus for my system the manual says that I can use up to 1333(ram) MHZ for the system depending on the processor.