I'm getting back into working out, it's been awhile quite awhile...... I'm trying to make it a goal in my new routine to preform a set no.# of reps within a time limit of 30-60 secs. I'm using relatively low weight with 2 sets of 6-20 reps each exercise. Right now, I'm using free-weights. So, I want to know should I used machine weights to achieve this goal or stick with free weights?
The answer to this question, almost regardless of your goal, is "Stick Wtih Free Weights!!!!" With that said, I'm with Ikken...why are you shooting for the most reps in such a short time? It won't get you any faster, since you're using such light weights. I'd rather see you use a moderately-heavy weight, and do a bunch of low-rep sets.
To be defined, speed, and work the respiratory. I do a list of compound exercises in a circuit form with set number of reps. I'm only doing two circuits as of now, and also rest inbetween the circuits atleast 5 mins. Though, I don't plan on keeping this routine for a long time.
Plan on ditching the routine now if I were you mate. Save the weightroom for power and strength work and use the dojo to work on your speed and endurance.