I've never heard of anyone ever saying an R1 is sluggish, never ever ever.
Bottom line, a 600cc has easy, usable power up to 100mph, a 1000cc bike does not, you either pull the front up or spin the rear tire. you simply can't get on a 1000 like you can a 600, that is why 600s with the right riders are just as fast and in many cases can be faster due to not having to be so light on the throttle, last thing you want to do coming out of a turn is a nice high slide due to your rear tire breaking lose thanks to the massive extra torque
As far as the 636 cheating with the extra 36cc? I've never heard that either, even more so since you can't cheat due to the 636 never being placed in a 600 class, they were hoping to pick up new riders due to the bike making better everyday street power.
No doubt if I were to buy another bike it would be a 1000. Only reason I would want a 1000 is for better midrange power and not having to keep the rpms so high if I'm driving on the highway to work. Would it be faster then my CBR? in a stright line sure, but on the normal US roads, ha. I'm lucky to see 3rd gear. then again I love hitting nothing but backroads. small tight backroads.