You touched on several good points
Using a smaller turbine will come on earlier but it will also reach max cap early.
Go larger on the compressor and it will lag.
There is a fine balance, again as you mentioned- it is best to design it where you intend to run it..Turbo shops will do this.
Street you will want to boost early, to bring the power on for street riding racing wtfe.
For faster spooling on the street racing scene, Velo was using the GT25 & GT28's & MCX used to use the K27/K26 modded turbos and since went to another which I don't know, TMH was using the T3/T4.
Your larger systems use the GT30,35,40 variants all the way up-
My turbo Turbonetics T61 was chosen for a few reasons, mid 500 hp (not that I may EVER even see or use it) I wanted to have plenty of power on tap to try my hand at top speed racing.
Whether or not it will ever get used for that purpose has yet to be seen.
When I picked this setup, I did my research, I talked with Seb & he told me what I needed to know, as well did 2 others.
The T-61 is not a T61 alot of people mix them up.
My T61 has had no problem spooling, probably because I am not running an AR on the turbine the size of a big assed woman either/
But no it doesn't run like the K26/27 setup I originally made either- two totally different setups, 2 totally different intended uses.
I talked with Turbonetics about what I wanted, and they helped me make the choice of turbines.
The turbo will support mid to upper 500hp, yet is still streetable without being like a pogo stick on roids like the K26 was.
but as you mentioned- you have no idea of my intended end use of the system I designed.
Pick your poison, build it YOURSELF if you want to or BUY one form a vendor if you want to.
I can tell you a million reason why you shouldn't do it from my own experiences, as well as most anyone here who has boost.
Build or buy it, if you buy it buy from Richard he is a top notch guy, or of course Seb if you can afford him.
I cannot afford Seb, so I built mine, then recently started upgrading parts from Richard and others who are upgrading their own.
I have watched Richard on endless posts and boards, answer and give help to people who have bought others kits as well as his own, including myself.
Hell look at this board and others, alot of good info here, and experienced people for building your own if you choose.
But I cannot forget as you said many times,
"Turbo bikes are not for those on a budget."Speaking for myself, mine was built on a budget & I may not have endless cash like some, but I still enjoy the HELL outta my kit, I made myself.