Raw you have a LGA775 socket so its core 2 and core2 quads only for you. You cant fit a any thing other than a LGA775 chip in there
and then its only what you M/B supports in its Bios.
i3 and i5 / some i7's are socket LG1156
The full fat i7's are on LG 1366 and triple channel DDR3, which makes it all a bit pricey lol but nothing is faster.
What chip you got in it at the momment RAW ?
The X48 was a high end chip set when it came out made for overclocking by the way.
If you have DDR3 ram an i5 750 & M/B upgrade would only cost you around £250 or less and this chip will run rings round any core chip.