i should start off by saying that you can't go wrong with a 600. these days they have plenty in them and i highly doubt that you will push the bike past its limits.......but if you are like me, it is nice to have some extra power. I have a '03 600 and '03 1000. A friend has my 1000 which i have pretty much sold to him, so i have been on the 600 as of late. i have a lot of fun because i can push it a lot harder without the added stress the 1000 brings. The '04 600's have plenty in them to last you as long as you have the bike. Now on to the GSX-R750. That bike is sweet. At only 5 pounds heavier than the 600 and over 20 extra horses, it will stay right there with the liter bikes and eat them in the curves. Everyone thought the 750 would die with the open class racing, but suzuki has shocked everyone. Most likely the bike of the year.....I am fighting myself on not running down to powersports and picking one up. The 750 would def be my top choice, but all the 600's have plenty in em. Hope I helped out......if you pick up this months sport rider (or maybe motorcycle mag) the 750 is featured....might want to check it out.