Hi,
We do not have the GPH specs, we do have them for the pumps themself, but not after it's modified, but the basic difference is the OR2700 is an Ocean Runner 2500 pump and the T 1000 multi pump is an Ocean Runner 2500 powerhead, so it's a smaller version pump.
The performance is probably pretty similar, the powerhead is just more compact so it looks better inside the tank.
thanks
jason