Why nittos? because I have pissed away plenty of money on different brand tires Goodyear, BF Goodrich, Firehawk Wide Ovals, Nittos, Sumitomo HTRZ,  and Dunlop, and I can tell you nothing can stick 500-600HP down like Nittos on the street.  There may be better options for the track like MTs but, honestly they will see very little track time compared to street.

I have tried all three Nitto 555R tire sizes now and can give some insight to those trying to make the decision. It is important to note that Nitto did not produce the 305/40 18 when I bought my 35 and 45 series, hence the size swapping. I guess Nitto realized there was a pretty big gap between models too.

First: Nitto 555R 305/45 18 on my ROUSH/GT   28.78″ TALL (way too tall for me)

Second: Nitto 555R 305/35 18 on my 2008 Shelby GT500 26.42″  Nice but smaller than the 27″ stock goodyears and it shows with the big wheel well gap

Last try: Nitto 555R 305/40 18 on my 2008 Shelby GT500 27.72″  Just about perfect, not too tall but fills out the stock wheel well with room for an FRPP handling kit. WINNERS!!!

Slideshow of all three.