ok, this is what I use for temps and stability, realtemp which you all ready have, Intel burn test for stability testing(prime takes way too long for me), run the test with maximum ram for 5 passes of the test, if that passes try setting to 20 passes, I find it finds instability much much quicker than prime95, be aware it may produce slightly higher temps than prime95, and I like to be below 75c for my i5 750 cpu
for connecting the extra fan you may get away with using 2 screws from the four on the original fan for now, just depends how you have it set up if you can get away with 2 screws either side, just be careful with your new screws that you dont screw in to far and puncture the radiator