Your memory would easy hit 890Mhz like mine, and I have DDR2-800. Memory can run higher than it's rated speed, you just have to give it slightly more voltage.
Going from 3Ghz to 3.6Ghz will show you an improvement in CPU intensive applications such as video encoding, some games, photoshop, etc.
For example.. I was turning an AVI into an MPEG4 for my Playstation 3... at 3Ghz it took 30minutes, at 4Ghz it took 8minutes.
So yeah... go into Bios, set your FSB to 400, after that you can decide if you want to go higher, because you can.
Set your Vcore to about the 1.3Volts area and stress test it.. If there is an issue or it doesn't boot, raise the voltage to 1.32V and try again.
Download Orthos if you dont have it in order to test your CPU and memory for stability.
Also make sure your memory is at it's rated voltage. If they are supposed to have 2.1V or 2.2V, make sure they are getting that. Mine are rated for 2.2V but when I first got them they were set to 1.8.
Let me know if you have any issues.