Heat is bad.
That said, we all know that the cpu is the hottest part, but there are other areas that need attention too:
Northbridge is one. Years ago, the nb on a mobo wouldn't even have a passive heatsink on it, yet nowadays even cheap ones do- and the best boards have a fan on the sink
One of the first mods I do is to remove the nb heatsink, lap it and reinstall using nylon nuts and bolts (from the nearby hardware store) and thermal compound.
It may not help a lot, but from my informal testing it does help; at least one or two mhz worth on the fsb, and maybe more.
Keeping cool air flowing over your ram seems to help as well. Neither of these components get as hot as a cpu, but cooler running is higher speed/better satbility and or longer life.
A high case temp hurts as well: it keeps all the components warmer- target for my case temps is within 2 or 3 degrees c of ambient, and if I'm not less than 5 or 6c I get annoyed with myself
I am also not scared of voltage when overclocking
. My water cooled rig runs cou vcore @2.05v and ram @3.4v. High, but I keep lots of cool air circulating, and I keep the case temp WAY down.
Only thing I water cool is the cpu- case temp is cool enough to take care of the rest.
If the temps and 5v line are good, then it will probably be a pci device stopping the fsb from going any higher.