It all depends on the setup.

Wouldnt you figure that is why a lot of TT Supra people go a huge single turbo.. TONS of variations here..

 

The reason we do this is primarily due to simplicity and the fact there is almost no benefit to a twin setup over a well matched single. Some people run the HKS 2835 twins, but they are far laggier than a single producing the same power.

 

True, but if you have a big enough wastegate you can very little or possibly no boost at all throughout the rpm range.
Edit: One thing that should be discussed is mechanical effeciency. TT's have a lower rating due to the two shafts (2 turbos vs. 1, 2 sets of journal and thrust bearings) and therefore more friction...even though friction is pretty slight with modern day ball bearing turbos, at 150,000 rpms a piece there's going to be some loss.