Ok...first off , if you had your HTT up to 225 and it wasn't stable why would you go to 250?
Also, the chances of frying your chip are fairly slim now-a-days. I pushed 2.225v vcore through my chip trying to get 2.8GHz remotely stable and nothing happened to it.
This isn't to say nothing ever can happen to it, because things to happen but still you're in the clear.
Like I told you in another thread once before, raising the HTT beyond 200 is overclocking your RAM. I can pretty much tell you unless you've underclocked it or have been tweaking your RAM timings and Dimm voltage, that is causing your instabilities.
Also like VIII said, more Vcore is needed for a stable CPU.
All this is covered in the OC'ing basics, so like I tell everyone who just dives in you need to really read up on this stuff because raising the Vcore for stability should be common sense when you want to go to overclock, not something you learn only after pushing your system limits.
VIII it says PC3600 in his sig, so considering it's that speed those timings are about where they should be.