It took me a few years to learn that personally my legs react VERY well to higher reps with a moderate weight. I learned this from a good friend who competed in England. Once I started shooting for 15-20 reps on all my Quad exercises, I noticed dramatic changes! For hamstrings, I believe heavy weight is the way to go. I like the 8-12 rep range for hams. Give high reps for Quads a try for a few weeks and see. I used to do 5 sets of 20 reps twice a week for squats when my friend first showed me this. It was brutal and I felt like a wimp with so little weight on the bar, but damn did I finally develop that sweep I was looking for! Of course you can't keep that type of training going for long, I only did it for a few weeks to break a plateau.