-f is for priority processing, the lower it is -f 0 the higher the priority, so -f 60 is not very concentrated processing. If you have a dedicated cpu for mining, then you would set -f 0 or 1 or 2, if you use your pc for other things as well, you might want to try -f 60 or above

I don't personally use diablo miner, but that's what -f does in the other miners

good luck!