I asked that question because I wanted to know if you're using heavy enough weight to get close to failure, and it sounds like you are, so that's good. If you're looking for muscle growth, then sets of 8-10 reps are usually good. You can also experiment with different rep ranges like 6-8, 12-15, etc. since everyone responds differently.
What I do is alternate between heavy weeks and light weeks. On heavy weeks I lift amounts where I'll reach failure in the 8-10 range, and the following week I lift in the 12-15 range. I've seen better results with this than I did when trying to go heavy each time.
Something else you can do is split your leg workouts into a quad day and a ham day. This way you'll be able to hit those muscles harder AND give them more time to recover. Along with sufficient stimulation, muscles need sufficient rest so they can repair - that's when they grow.