I can tell you this. I don't have any experience with the 2.75 in a high HP application. When I was putting my 400 together and researching the different parts available, while talking things over with a supplier I have gained alot of trust with, I mentioned the desire to use a 2.75 gearset in my anticipated 1,000 HP application. He quickly talked me out of it. Not strong enough. I went with a THM475 gearset.
As a race car's HP and torque level increases, the importance of having a low initial gear ratio decreases. Especially if the car is traction limited (10 inch slicks). Small turbo engine in a big car, it does help get that turbo spooled up a little quicker by getting the engine into its' optimum operating rpm band sooner. But then, that is why God gave us the juice.