I was still thinking about single turbo vs twins and it looks like most of performance cars using turbos are using more than one as a setup. I actually haven't seen any high hp stock cars using single turbo...
However twin turbos include:
911 tt 3.6 480hp
GTR V6 3.8 545hp
M5 V8 4.4 560hp
E63 AMG S model V8 5.5 577hp
Bentley W12 6.0 600hp
Saleen S V8 7.0 750hp
Veyron W16 8.0 1001hp (quad turbos)
Barabus TKR V8 6.0 1005hp
Ultimate SSC Aero V8 6.3 1183hp
Then you have some underground cars that put twin turbos
On lambos, R8, GTR and they produce 1000-1500hp...
So, I don't know much about turbos, but the industry
seems to have adopted the route of twin turbos for what
I have seen...
Cheers!