I installed a hybrid gt45 about two weeks ago. I had to fab everything including pedistal, oil lines, intake manifold, intake tube, up pipes and y, down pipe. It is considered a large frame T4. From all the information I based it on my stock injectors would not spool it. That was wrong, I can spool this turbo fairly easily, it does have a little lag at low rpm's but it is much stronger at high rpm at that was a trade I was willing to accept. I pull a heavy job trailer and sled pull with truck. I just drove it to NC this week for work with no problems. It seemed to be easier on fuel but I haven't calculated it yet.
Every powerstroke I have ever had was slightly modified (tuner intake exhaust) and every one ran poor at the top end. Now I am finally pleased with the performance above 2700 rpm. The reduction is back pressure is massive compared to the stock turbo. 68psi backpress at 25psi boost stock, 35psi backpress 30psi boost hybrid. I think this is the major factor in high rpm performance. This is both with the same tune and injectors. NO SURGE even when I lock up too soon.
The turbo whistle is extreme however, almost annoying from 1500 all the way to 4000. When it goes over 20psi it is almost as annoying as the ch-ch-ch surge noise.