Well, as far as i know turbo cars are faster with auto tranny,the reason is that during shifting gears RPM in auto drops less then in standart transmission.If you look for 280zxt performance date you will find that auto is faster,so this is true.
Now you can leave your turbo auto tranny,but you should swap rear end and CV joints too,or you can leave original 5spd in your n/a you will be just fine,i'd update differential with R200 4.11 though.Car will be faster and still get low RPM on freeway.I'd update to Cv joints in anyway,no matter what tranny you will be using.
So it's up to you what you will put.Just remeber that it's a good time to rebuild tranny if there are any problems.Just my .02