Mine is the Rockwell 6S.
I've owned the 6S for around four months and absolutely love it. I've tried all the plates and found the best for me, is plate 6 for all three passes.
I've tried quite a few combinations with it to (still have three or four more blades to try, Feather, Perma Sharp, Rockwell, Voskod), but I have found the two I like best so far are the Astra SP, Shark.
Personally I've found that even with using the most efficient/aggressive plate for all three passes. I get no irritation/razor burn, due to me not having to go over the same area anywhere near as much as I did with a lower number plate. Sometimes using a more efficient/aggressive razor, can give you less irritation/razor burn, than a milder one, due to it removing the need to go over the same area as much.
I really like the heavy weight of the 6S, as I find it much easier to use only the weight of it, and no pressure, as opposed to using a light weight razor and then having to use and remember how much pressure is needed to get the thing to shave, and shave comfortably.