You have to factor in how much current draw you have from your cars components also... Adding an additional load to an already weak electrical system can cause problems. I've had a car with a 90 amp alt that the lights dimmed badly with ~1000 watts. The same system was on a stock 65 amp alt and I got little to no dimming. All in all, it's hard to say for sure how much your electrical system can take. You could try to do the big 3 and add a second battery on your current alt and see if that works...might be the cheaper route in the end...