This may sound dumb, but try it. Turn your back two fans around to blow into the case, and turn off the front fans completely just for the test. If possible, aim one of the intake fans to blow either directly on or across the top of the HSF for the proc.
You have a lot of air pull out of the case, but not a matching amount going into the case. I like to run mine at positive pressure to help keep the dust down. Also try rolling your IDE cables if they are not already. This will aid clear air flow like you wouldn't believe.
A 1.2 T-bird does make alot of heat, but you should still be able to keep it a little bit cooler than this, and without those wide ranges. If you can stand the noise, get a Delta Black Label. Sounds like a jet but it turns 7000 rpm too! Amazing what a difference it can make.