i recommend against using speedfan for things other than case fans...
Reason being, you need to be loaded into windows for it to be working correctly. It's kind of annoying to tell you the truth.
To answer your question, the 800 should be fine for cooling the CPU. The slipstreams move a lot of air for what little RPM they run at..you will be surprised. That said, you also have the following option: you can pick up a 1200 RPM slipstream, and a Fanmate
. The fanmate will allow you to "set it and forget it" after an initial trial and error period with various speeds. Try turning it up to a point where you can hear the fan, go a little slower, then benchmark your CPU. If core temps stay below 60C after 10min or so, just leave it at that speed, and forget about it forever! (that is until you do a little housekeeping in the case).
That said, I still believe the 800 is fully capable of cooling your CPU. Hope this helps..