My recommendation is that you don't think in terms of slower/faster since speed is predicated mostly on how efficient you are with your technique and movement. Many consider a dropweight more tedious, labor intensive, and that's what eats up time by in large. Your situation is a little different than a lot of people who don't own a machine in that you're currently stringing racquets, and doing it on what is considered a fairly nice machine. My guess is you probably don't want to take a step backwards in terms of efficiency/convenience features, and in my opinion, that's what a dropweight would be.
Since you have a budget of $500 your best bet is to scope out a used machine.
Need help finding lost dog: walks with a limp, recently castrated, can only see out of one eye - answers to the name, "Lucky".