Everyone is different. IMHO, you should set the number of reps based on your body and not based on some arbitrary number that works for others. In my case, I had been doing a large number of squeezes and therefore started with 15-20 supra slammers (and worked up from there). FYI I usually start with ~10 min jelq to get loose and some flaccid bends. This way my penis starts expanding right away. Without the jelq warm-up, it can take 10-15 reps before my penis starts expanding. I do as many reps as my penis is comfortable with and I stop if I start getting fluid build-up.
I gained a little more than 1/4” permanent gains in the first month but had to stop due to a hand issue.
11/20/2011: BPEL: 6", MEG: 4.75" (goal BPEL: ~7", MEG: 5.25")
5/9/12: BPEL: 6.5", MEG 5" (goal BPEL: 7.25", MEG: 5.5")
3/5/13: BPEL: 6.875", MEG 5 5" (max goal BPEL: 7.5", MEG: 5.75")