A 600 or 1000 I4 will not be as forgiving on the street. I have just as much, if not more fun, on my small <500cc supermotos than I do on my 2008 CBR1000RR. I am selling the 1K because it is highly impractical, expensive to insure, poor on fuel relatively speaking, and not as versatile. With my WR250X I can do just about 200 km for $7.50 of 91 and my insurance is 614 a year.
Straight line acceleration is but a minor part of riding.