well... I think the initial pick up/ spool time will be slower maybe 100-300rpm but billet wheel may now cancel this out being lighter or maybe not as it grabs a bigger handful of air every times it spins which requires more torque/force from the exhaust wheel. BUT once the slightly bigger turbine wheel starts building boost, that bigger diameter wheel has much more leverage force which in turn gives that compressor a larger more rapid shove to reach its intended rpms for better on boost response.
There's less restriction with bigger turbines as they are better at expelling the wasted exhaust gases without choking up the exhaust side just like a small exhaust system would slow down your compressors ability to ramp up FAST.
which affects RESPONSE.
Thats why -7s -9s -5s are so popular and gt2871 or -10s are not.
I had a 2871 it was good for outright power but choked itself to death after 1.4bar and that was a .86 rear housing too!
hope you can understand why sometimes slightly bigger exh wheels not too big!
can work in our favour
sorry if I rambled a bit too much tired from work.