My point is that it's doesn't make any sense to have that much alternator on a daily driver. You won't use probably half the capacity, ever. Even at lower current demands, the bigger alt is going to be more of a load on the engine as well though not probably that big a deal with a V-8. It's not like you'll make the mileage on that thing much worse.
Back on point, I would think that something in the 200A range would be more reasonable and affordable. If money isn't an issue, knock yourself out, both with the alt and with the pair of 2500's. You won't use all the power, but you won't run out either...