Do you really want to limp around town with basically n/a Grand Prix until you can get that turbo spooled in your upper rpm range?
Spool speed is pretty dumb to talk about.. brake boosting/antilag will put a 61 and a 67mm turbo on the same playing field in terms of spool speed. The 67 is a bit laggy in first gear, and most cars will not see full boost until late in 1st gear without a big PSI launch. My old T3 turbo fiero setup would make full boost in ANY situation as long as I could lay a tiny amount of brakes on it... antilag works quite well for cruising around.

Driving my T67 GTP around I never brake boosted or antilaged it.. and i never ran more than 14psi because it was stuipid. I never drove that car to race it really, because it just was a completely usless vehicle for that sorta stuff.

With turbo, powerbands dont exist.. If you have the pedal down, you make as much power as your wastegate wants you to make... Every dyno sheet from my turbo cars showed peak power when the boost spikes a psi over target at 4200rpms.. otherwise its dead flat... This was tested with modified timing camshafts, big cams, small cams, big turbos, small turbos.. its all the same.