If you mean the likes of the Minolta, 787B, Sauber C9... then no, it's not really a good idea to give these cars 4 digit horsepower figures. Unless your chasing top speed of course. But out the box these cars are already fast. You'd just be increasing the tyre wear rate by raising the power.
The other thing that happens when you go with a Class 3-4 Turbo is you increase lag a lot.
Then your power comes on hard at the most inconvenient times.
Since you've got your answer, this thread has run it's course.
The other way to find out would've been to actually try it for yourself. 💡
Buy stage 3 & 4 turbos, don't save the game and try driving the car in stock form and then comparing the performance with stage 3 turbo and stage 4 turbo fitted in turn. If you like either reset your console and buy whichever you feel is necessary, if not reset, don't buy any of them and you've not lost any money since you didn't save anyway!
(Assuming you've got autosave turned OFF, which you should definitely ensure, since it can inadvertently lead to save corruptions )