you can go alot farther but you are going about it all wrong. The propus is a locked multiplier chip meaning the Referrence clock/FSB is the main indicator of OC as opposed to the multiplier in Unlocked chips. OC'ing locked multi chips must be done in a process to ensure maximum stable OC.
first thing set everything back to stock. Go to your memory timings and set back one standard(1600 to 1333) or what ave you. Start bumping the reference clock(FSB) up 5hmz at a time until you become unstable. My REF/FSB is at 240=3.6Ghz No voltage increases VCORE:AUTO 100% stable with this method. Only once you have found your max with adjusting only the FSB you begin to adjust voltages and other timings such as VCORE/NB VOLT/MEM VOLT/ HT LINK to seek stability with further REF CLOCK/FSB increases.