I have to say that the exhaust fan at the front theory could not work*, due to convection, as paparazi points out - hot air rises. There are many "expert" articles around the web which make that point, and all my tests have indicated that the theory I have suggested is good in practice by up to 10 degrees.
*Unless there was an exhaust as well as an intake, as a couple of articles over on
suggest, with possibly a passive vent at the side, instead of an additional fan.
If you've got any links to prove your theory, I'd be most interested to read them, Thelemac.
Also, the space around the back of a computer tends to be smaller (and gets warmer quicker) than the room in front of it - try putting your hand behind your PC and see exactly what I mean.
Airflow inside the case is what is most important - Keeping a stream of cool air over your warming components.
I suggested the shim, because, if you've whipped the heatsink off your processor, sooner or later you have to put it back. This greatly increases the chance of damaging the CPU - especially Athlons, but a shim will keep pressure off the processor and, for a few pounds, is a worthy investment. I've even read reports of temps dropping after installing a shim, but in theory, since they sit on the ceramic, it makes no difference.
It will certainly transfer heat to the heatsink, if installed correctly with thermal grease applied - but, guess what? That is what the heatsink is there for - it dissipates heat. Anyway, it is an insignificant amount.
I forgot to say, if you are applying thermal paste, remove that horrible pink rubbish that most heatsinks ship with - it's useless.
As I said in my first post, 50 is not bad at all - I just like to keep my own Athlon processor below 40 at all times, so even if my theories are proved wrong I don't mind - my computer runs very cool
CitrixEngineer@yahoo.co.uk