4 Plates!!!......I believe in pyramid sets so go 2 1/2 plates and then 4 plates 6-8 reps, 5-8 sets and then 3 plates for 2-3 sets and so forth...and it's off to the sled, etc.......I could go higher, but it's not about weight as much as it is about stressing my quads, and I train alone.
SQ-