I think there are several issues to look at here, so lay down the tools and the wallet for a while .
1# What's the "stock" operating temp for a P450. My stock HP P300 if I remember, runs warmer than my P750@915. The P300 hs has no fan. An 80mm fan on back blows baby breaths to it via plastic shroud. The shroud is not even in close proximity of the slot 1 cpu. Even then it will OC to 360 or so as it is.
2# Is the 52C correct? If the heat sink will cook your finger if left there long enough, then most liky it's in the ball park. If you can't tell if it's warmer or colder than your finger, then the hs is around 36-37C. Offcourse the actual chip will be slightly warmer.
3# An 80mm intake fan wallops a lot of air. I'd make sure this air is put into good use by giving it a way out through the back and/or top of the case instead of the vents in the side panel. To help the front fan, maybe three 40x20mmm fans stacked in column will fit in the back near the top.
4# If nothing else,
a) I'd give the 450 a better hs/f if you ain't got it already.
b) This could be controversial. Make a hole on the bottom plate of the case and move your 80mm fan there. Let it blow air upward between your cards and the back of your drives. This will really create mega turbulence inside the case with one fan and flush the air via the side vents, front vents (now empty), etc. Also open a couple of slots in the back if you have them and have not installed any fans in the back. No fan/s and no vacant slot? Drill. This might be quieter too than a front or side fan setup.
I hope I understood your question correctly. If my answere is way off, sorry .