different beasts completely. The R6 had more in common with the R1 of the time than the 600R. The 600R used to be the sporting 600 of Yamaha but was getting out classed badly by Suzi + Kawi, and out universialed by the CBR, so it became the "sport tourer" by default.
The R6 had cases like the R1, fuel injection and (basically) better everything. The 600R was more like the FZR (and thats not bad). I think theyre still carburated to this day, but theyre not bad bikes at all.
The R1 and 1000R have a similar story only it happened a few years before the R6.