Adding heavy lifting to Body Pump?

I already go to Body Pump 2-3x/week and do decent weights (e.g., 40-50 lbs. for ~100 reps for squats; 35 lbs. for chest press and back tracks of ~100 reps each) but I'm thinking of replacing one Pump class with a heavy lifting session. (I want to keep going to Pump regularly and not give it up completely since I get great results and really enjoy the music and instructors.) Where might I start weight-wise to lift heavy (and how many reps)?