with proper gearing and decent batteries probably around 50 is possible. I run a 5.5 with basic GP3300 stick packs in an hpi rs4 rally, and it will go about 40-45, so maybe if the tc4's drivetrain is more efficient (which I think it may be) and using a faster motor, you can go at least 5 more mph than me
gearing is different for different cars, but I find that the 5.5 runs best with my rs4 using a 24t pinion and a 90 tooth spur. if you are using the 4.5, you will gear it slightly lower than what you would gear the 5.5 motor. there are lots of people who drive the tc4, so finding gearing advice specifically for that car shoud not be difficult.