I did my last test on 240, i wanted to run this cpu at lowest voltage at 2.8Ghz. I run torture test (vcore 1.3V/stock 1.4V) for 12Hrs or so with no issue.
I had got a chances to exchange this CPU with new 550BE, so i took it with both hand. Next day i got my 550BE, set required setting, and damn i couldn't be any happier, it was fully functional quad. I'm doing various test with that chip now, been running torture test for 3rd day straight changing settings every 12hrs of successful run.
As much as i like my Athlon II 240, i always wanted to get 550BE. I never thought i'd have change 240 so early( about 3 month). Its such a great chip for 60-65$, get all the job done cheap and really fast. I think best bang for buck chip i ever got.
My personal rating for this chip is 8.5/10.