I'd go with Tim on that one.
I ran winch, 5 spots, compressor etc etc with a 75amp alyernator and a red top optima for two years with zero problems.
I only run two optimas now as Im doing comps and when your winching 20 to 50 times in a matter of a few hours you need that extra battery!!! :)
If your not doing comps, get a top battery in there and up rate your alternator is probably the cheapest and best long term solution :D