CPU Bottleneck when recording?

I am not sure if it is my CPU or Hard drive but when I record with fraps at 50FPS my FPS on minecraft drop to 40, it can go lower than 40 but it won't go higher than 40. Is this my processor giving the bottleneck or is it my hard drive, I am recording and playing on the same hard drive. If I were to buy another hard drive would one with 16MB cache be enough for recording of should I go with one that has more

PC SPECS
Intel Pentium G850
AMD 7770 (13.1 drivers)
500GB WD SATA 3 7200rpm
8gb ddr3 gskill ram (irrelevant but posting)
500w PSU (irrelevant but posting)

Thanks for your help everyone!