I believe the max temp is about 160f for an Intel, and with your 140f you're getting pretty close to that.

I read an article which showed that Intel's own built-in protection (the thing that'll slow down the CPU speed gradually based on temp if you enable the feature) kicks in around 172f. So yeah, I agree, I'd tend to want to keep it under 160.

Last night I tried putting in a makeshift duct which routed air from outside the case directly onto the CPU, then played a bunch of Unreal 2 with the case cover on. It worked great as far as keeping the CPU temp around 140f. And the motherboard temp didn't get above 115. So I was happy with that. Except then the problem became the disk drives. After that session, I opened the case and all the built up heat had made the drive casings hotter than I'd have liked. I'm going to investigate some case fans.

I also had another idea, that I could do a pairs of quiet 40mm fans in certain spots on the case that don't accept an 80mm fan. I remember seeing somewhere an ad for a very quiet 40mm fan, I'll see what I can come up with.