pump configuration

Yes I know ballast systems have been questioned to death but I have I guess a different question. Right now, I have 3 attwood 750s for each of my sacs. the only problem is that they best place for them, right by the thru hull, couldn't be done. So the pumps have about 1.5-2 feet of plumbing and valves and such before the water gets to the pumps. Now I want to use sprinkler valves, and so far they have worked quite well since the valves are mounted on the pumps. Here is my question. Will I gain a substantial amount of flow if I take out the three 750s and put one 2000 right on the the thruhull? And if so, will a 1in thru hull and 1 in to the manifold then 3/4 be enough to handle the 2000 gph pump? and last question, where is the best place to get a 2000 rule/ cheapest? thanks and sorry to drag the ballast questions out