What do you suggest I do now to push the overclocking further to find the wall of my system?
You lower the CPU mutiplier (10 or less) then raise the FSB till your ram craps out (memtest86), then raise the mem voltage and try again. You'll hit a limit then back off below the limit and bring the CPU multiplier up till it craps out...simple

When you use Prime95 set it for the "Blend" test and if it runs 12-24hrs without crashing then you should be pretty darn stable.

BTW for you to get the most out of your system you'll need better ram that'll do 250+FSB, your system is pretty powerfull the way it is so be happy