Mitshu 3000GT, Dodge Stealth, Nissan 300ZX, Nissan Skyline GT-R, Toyota Supra, need I name more?think about all the fastest turbod cars
The only reason there is a sudden burst of "new" 4-cylinder turbo'd car's, is their cheap and easier to work on. That doesn't make them better. There is no replacement for displacement, either turbo'd or otherwise.
The main disadvantage of a 4-cylinder turbo is the lack of umf prior to turbo spin-up..when out of the boost range, a I4 is significantly slower then a standard NA I4, simply due to differences in compression, timing, and fuel...so if you go gung ho, and slap a big ass turbo on one, your going to be fast sure...but its just as possible that little instant torque monster electric hybird is going to kick your ass off the line.
An excellent example of this was last weeks autoX in manassas, VA. The EVO's and Sti's were utterly crippled by the size of the course, unable to bring any amount of boost into play, and for more then half the course, were running without the turbo's spun up, allowing such car's as the much lower hp Mazda 6i MTX, to totally slaughter them.