I am starting to get together parts for my 12a turbo set up. I am looking for a very well balanced turbo, to use mostly for auto-x so quick spool/midrange power is a must.. The motor is street ported with a 465 holley and rb intake currently with full non collected RB exhaust (duals).. I plan on starting with a blow through system and eventually going to F.I... what size carb will i need?

What type of turbo should i be looking for?? I am looking for 250-350 whp but it needs to be very smooth.. I don't want to break loose coming out of every turn.. I will be running an msd6al for ignition and a locked disty.
If i have to sacrifice top end for response than thats what needs to be done, but i need to know what type of frame and ar ratios to look at, maybe the upgraded s5 turbo from rotaryshack? point me in the right direction fellas, please..

All my tuning tools are on order, the motor is being rebuilt very soon.. and I am itching for more power.. I'd like to get the turbo set-up done before the end of this years auto-x season to see how it will handle..