The gc isnt important in minecraft (just for shaders).
First u could try to overclock the CPU ur max speed is 3.3Gh in High speed
Also another recording program: I used OBS for a long time and my recordings were 30fps recordings. (i have the i5 6600k gtx 970 and 2 250 ssd´s so that shouldnt happen)
I would recommend LOILO for recording:
http://loilo.tv/de/product/game_recorderAlso u could delete old apps u dont need so that ur disk is not overload.
i hope i could help
