e8400 has higher default multiplier. just lower dram divider and push fsb.
increase vcore a bit for stability and watch out for temperature if you still using intel hsf.

last time i try q8400 can achieve 3.2ghz --3.4ghz, not sure about 3.5ghz if your cpu can keep up

from 333fsb push to 400fsb
multiplier keep 8x and use 1.3 vcore. remember to reduce memory divider so your ram wont over speed

prime i like to use blend test, or try another program call OCCT