I was idling with that chip (stock) in the low to mid 40s but I'd never built a computer before and didn't use paste. So I put paste on and made sure the heatsink was on firmly and now I idle in the low 30s. To me, your temp is a little on the high side...
Are you using TAT to get these temps? What are the temps while hardcore gaming?
Mine idles @ 37-44, no extra nothing (retail heatsink, no extra fans in the case etc..).
I have no idea what's the temp in my room right now, but overall in the city is 25C. (My room right now is like @ "ambiance" temps).
I was idling with that chip (stock) in the low to mid 40s but I'd never built a computer before and didn't use paste.
no paste!!!! lol. You scared the hell out of me there...
I found that my 6600 was quite affected by the paste that I used. I bought the sticky white type (which you seem to need to use a lot of, I used the gray gritty stuff before that, even when it was white it was gritty and not tacky) for the first time and I found I had to redo it with more paste, dropped temps dramatically, particularly during load.
I knew because I had an better cooler that I installed that the stock one, so I knew it shouldn't have been in the 40's plus the fan was at high rpms too often.
In a way, I think it's worth cleaning it up with Acetone and using more paste to start again in my opinion, particularly if the cores show too much difference in temps....
I have a Coolermaster Hyper TX as tom's suggested and temp is 27, and it's quite chilly (maybe 17c here) not really on idle.