Now that I have both an SL600 and Sl65, I found the SL600 with RENNtech engine mods has more bite than the stock Sl65. Both are fast, but the SL600 is more responsive and a little more fun to drive. It seems to ride more like a sports car too, maybe due to wheels since the 600 has 20" rims with smaller sidewall. I will know more about that when I get my 20/21 wheels on the 65. Some day will do the RENNtech on the 65 after I get over paying for the wheels. But for those wanting real bang for the buck, an SL600 with RENNtech is something to check out...scary fast, wear diapers.