You don't have to make massive jumps in vcore. Just remember that 1.55V is the absolute max you should go, 1.5 is probably for max safety (thats my limit on this pc). I just went through this the other day with a 955C2. I got stuck at 3.5Ghz. What got me moving again was dropping my ram speeds from 1600 back to 1333, the CPU was much more stable.
Once you get the CPU stable you can get the ram back to speed or tighter timings @ lower speed. So yeah, ram was the deciding factor in my being able to OC this chip. You should be able to get that thing up to 3.5ghz at near stock voltages. 1.55v is for attempting a 4+ ghz oc, and you shouldn't try that without a good cooler, and definitely shouldn't just jump from stock to 1.55v. Overclock in small increments, go up 1 multiplier.. see if its stable, if not try going up one notch of voltage etc.