I'd go with a manual fan over a temp sensor.
The sensor simply cannot be as smart as you.
Just play around with it until you find a good rpm that doesn't turn out an annoying frequency.
I have a smartfan2, and with the thermal temp it always did more work than necessary...
At load it ran at least 4200, and I run it at 3300-3400 keeping the same temp.
Personally if I were you I'd get the 800 and a quiet fan (panaflo or NMB) and leave it at that... that should keep you well under 50c and thats good enough for anyone. super quiet. If you are going to raise your vcore (which you will have to if seriously overclocking) you'll probably need something more powerful. This could be picked up later when if you decide to overclock higher.