i don't know the idle temps nor the playing temps but i when i bought it (second hand) it kind of heated a lot when i was playing, i idle is was good i think.
but yesterday it heated much more, that makes me think it's the thermal paste because it makes sense. first time i applied a good thermal paste but kept getting the ps3 apart and build it back again and so on( because of downgrading and stuff) and when i was done downgrading and installed cfw and tested it(with ps3 out of the casing) then i put everything back together and after i did that the ps3 didn't showed anything on the screen, just a few minutes after it worked. and it makes sense to think it was because of the thermal paste, because when i first applied the good thermal paste, it began to stick to the rsx and the heat sink, kind of glued together, and then i pull the mother board from the heat sink(in order to build everything back together after) the thermal paste wasn't as good as knew after that and after i build everything back it didn't made contact well with rsx and heat sink and that cause the GLOD. After that playerkp420 told me to remove the thermal paste and apply it again but when he told me that i was out of the good thermal paste, and then i used a "not so good" thermal paste, and then it worked, but just until today because the thermal paste wasn't good enough and didn't make contact enough today when i powered up the ps3(and the thermal paste(the poor quaility one) layer was thin too)
And that's my theory about it.
I don't think the RSX solderballs are broken or something, it's just the thermal paste and i think changing it and puting everything together and never removing the heat sink from the mother board will make everything work fine(the good thermal paste i was talking about was arctic cooling mx4, it's metal compound free and it has 8 years warranty)