I'll just throw this out as an untested counterpoint to the 100hp loss from the factory x-ram.
I dynoed a 12:1 RB499, ported Indy -1's, .650 lift roller, 2-2 1/8 headers, OE stage II manifold, FM carter 750's.
It made 675hp like that. I didn't test any other manifolds on it, but I just don't think there was another 100hp to be had out of that motor by installing a 440-3 and a dominator.
I suppose it might have made 775hp, but I know I've built "better" motors than that before that didn't get there.