I'm running the stock alternator and a single Optima Yellow top battery. Works fine for the occasional use I put it through...

I do use mine more heavily than most people probably do; I've put several (6 or 7) spools of wire through my Ready Welder powered by that setup, also run my compressor frequently, and a 2000W inverter, plus all the winching.  I even built a shed in a remote location powered completely with my sami...inverter ran the saws, and the compressor ran my nailers.  It worked for 2 days straight and I only actually ran it for a couple of hours each day (too cheap to buy a generator).  I actually went through a few 70Amp Napa rebuilt GM alternators before I bought the powermaster...had the powermaster now for almost 2 years and it gets worked hard but still alive and working great. 
My dual orbital/powermaster setup is probably overkill for most people...but it has proved to be nearly indestructible.