I would recommend a Y instead of a T, you'll get better flow. Also keep the Y relatively close to the top this will minimize double head pressure.
You're correct the little giant pressure pumps in this range output of 1000GPH a standard non pressure is 1225 which is better? I think its a toss up. Since you're not really pressuring through a venturi valve, you may get more flow/power with the non pressure model. I'm sure you could use either one- both would produce good results.