As much as I loved my 06 12RT, the 1200 and 1250 LC RTs never grew on me. Butt ugly, cramped ergonomics, loud engine, and not as nimble or precise in terms of handling as expected, compared to my 17+ k16 GT (big surprise on that account, while riding a 1250 RT on the same British b-roads as my k16). Wind protection was also meh, with some ugly helmet buffeting, in my case.
The engine performance is / was sweet, with plenty of punch and pulling hard all the way up into highly illegal speed limits. But the 1250 boxer platform, in any iteration (I did rode several RTs, GS, GSAs) is most definitely not a k16. The loud, obnoxious noise of the engine, when revved up was a no go, for me, for really long distance riding (I"ve learned this the hard way while owning a 17 1200 GSA LC, that I had to sell 7 months after purchase, after one trans-European tour - disturbing LDR engine noise was one of the top 3 reasons). The smoothness cannot be compared. I loved boxers for 15 years, but they now all feel agricultural, to me - I no longer get the "vibey, organic" thingy at all, these days. There is a feeling of elegance, precision, and steady peacefulness that the k16 exudes, un-matched by most other platforms. In addition, regarding power to weight ratio: the six cylinder power band is way more elastic than the shiftcam - you need to be very considerate of keeping the boxer in the right gear. The k16 will simply pull, in most gears, drama free. The quick shifter is really pleasant and useful on the big 6, rough and of limited use on the boxers. Regarding reverse: most heavy bikes (think engines over 1000cc) should have it as standard. And then there is the aspect of 1up vs 2up riding: when going 2up, the power to weight ratio is completely different, as is the overall weight balancing on the bike. The k16 is much more competent for 2up riding (the 1250 is no slouch, but it's definitely not as stress free).
Also regarding ergonomics: the 1250 RT ergonomics no longer work for taller riders, 1up, and they are less than ideal for 2up riding.
The combination of hooligan - gentleman bike, do it all street bike (for me), keeps me hooked on the k16, after all these years. As stated elsewhere, when it works (direct reliability reference) the k16 is unmatched.