You are better off installing a voltmeter and all your stuff and see where your voltages drop. Sh*t on paper almost never translate to real world performance, there's waaay too many other unknown factors that you cannot properly put into your equation. Such as actual alternator idle, vehicle power draw, box rise(which dictate ACTUAL current draw, you arent drawing 250 amps at all times, especially on music, meaning your amp will never produce a constant 2500 watts, if you wire to 1 ohm, best it can do is 500-1200 watts after rise on average not because its a bad amp or anything, its just how all amps work aka physics.), amp efficiency, battery reserve etc...
I ran 2400 watts a stock 80 amp corolla alt, with plenty of battery power, no drops under 13. While some other cars basically die out with just 600 watts.