G.SKILL F2-9600CL5D-4GBPI
-4GB (2 x 2GB)
-DDR2 1200
-Timings 5-5-5-15
-2.1v Rating

This is the best 2x2GB kit I've ever used. Very stable and yes very fast. Nowadays, this kit is very hard to some by. I got mine from a friend who got it from the US. I have friends at XS that are still using this kit. Some even run them higher than the rated voltage, but they don't even get hot at 1.25v. Just warm.
DDR2-1200 at CAS5 2.1v
DDR2-1100 at CAS5 2.0v
Specs:
Intel Core 2 Quad Q9650
Gigabyte EP45-UD3R Rev.1.1
G.Skill DDR2-1200 2x2GB