Pretty much all depends on your goals...but on a stock motor especially stock unported heads, a 61 turbo is about the limits. I mean you can go bigger but the heads won't flow it anyways so what would be the point. Now heads and cam is a different ball game.
I would agree with Don3d. (oh no, did I just say that?)
Go with the PT-61 with the 52e exhaust wheel. I loved that turbo. You should see some nice times once you get it tuned.
That thing spools like mad, and make great power.
Brian