Most E5200 can do the sweet spot of 3.6ghz. Others push it a bit more and run at 3.8ghz. 4ghz, while not impossible, is also unlikely unless you have good cooling and a good CPU that requires low voltage.
I would just look for a quality P35, as 965 boards are older. Both should be found for around the same prices. X38, P35 were designed for 45nm processors, 965 would require at least some type of BIOS update, some boards makers may not update BIOS for older chipsets.