well, looking at it logically, if you have a stereo for listening, not competing, then you will be fine. to elaborate, with class AB amps, even 500 watts will not pull much more then 40 amps, D amps will pull less per wattage but they scale to around 2000 watts...
if you have a standard subwoofer and internal speakers both off amps (averaging to 75x4 and lets say 300x2 for the subs) you should have no issue at all if you are close to this range. if you are putting down 150 or more to the front range, and 100 or more to the rear, with dual subs each recieving 1000 W, then i'd say you may need to get a higher output alternator, or possibly have it rewound for more amps... i think you will be fine personally. remember only when the stereo is cranked to around 70% does RMS even get reached, let alone peak numbers which a lot of people now a days have started using again.
Steeda or march seems to be the aboligitory choices. I personally will be getting the steedas down the road.
Torinath