BiTurbo:

Almost identical to the V8 TT from the Panamera Smileyand all 3 begin to run out of puff  between 6,000rpm ~ 6500rpm  Smiley

 

 

Because unlike McLaren who spec-ed their turbo to run all the way to 8500rpm, Porsche spec-ed theirs to ends around 6500-7000. 

Porsche's torque curve is more down low in the rpm range, improves everyday driving responses, it doesn't need high revs. 

McLaren's turbo makes less torque can rev to higher rpm.