Let me tell you my RT story...
I've been a long time ST1100 owner and fan. Got my first one in 1999, and traded to one of the last 2002's to get ABS. Still have it, and will likely have it for a very long time. I also have an 07 R1200GS that I like very much, and have owned several other BMWs in the past. I'm not a fan of any brand, Honda or BMW, just certain models.
After 11 years on ST1100, I've been thinking of a change. I did briefly own a 2003 ST1300 shortly after they first came out, but didn't like it, and sold it after a few weeks. I didn't like the heat, the handling, or the general feel versus the ST11. To each his own. That was quite a few years ago, and since then I've learned a lot about setting up a motorcycle suspension. I'm sure the ST13 was set up all wrong when I had it, so my opinions about the handling and feel were probably incorrect. You can make any bike handle poorly with the wrong settings, but I didn't know that back in 2003.
We had a 2004 K1200LT for two years. It was ok, but felt like we were in a car. No passion.
Several years ago we demo'd an R1150RT. Yuck. Engine was crude, no power. Both my wife and I hated it. Glad we had the ST11.
The engine in the R1200GS is quite different than the 1150. Balance shafts make it much smoother, although its still a twin. I had been thinking that if I could get a bike that rode and handled like my GS, but the body, luggage, and amenities of the ST11, that would be a great combination. Of course ,that's exactly what an R1200RT is.
I began searching for an ST1300 or R1200RT. A new RT comes only in silver or grey, which is not my color (sorry, I know many like it). I found a very nice 2008 RT in Biarritz Blue and bought it. Initial impressions were positive. The RT handles and rides very well (it has ESA), although not up to the Elka suspension I have on the GS. The RT engine has more top end than the GS version of the 1200, and the RT is geared longer (engine turns slower). The RT has good power, but gets into the typical BMW 4500 rpm buzz at about 85mph in top gear. I don't ride much at 85mph, but on the RT, 85 to 90mph feel strained. The power is there, but it isn't enjoyable. Of course, if you get it over 100mph, it feels good again!
My wife did not care for the RT, which was surprising as the RT is noted for passenger comfort. The stock BMW seat is even worse than a stock Honda seat, but we would have replaced it eventually. Coming from the ST11, she didn't like the twin cylinder vibes of the RT. She even commented that it didn't have much "oomph", even though she was riding on the back. Isn't it great when your wife says you need a bike with more power?! On paper the RT has enough power, but when you get 400 pounds of riders and another 50lbs of gear on it, you need the RT in the 5,000 to 7,000 rpm range frequently for good acceleration. At those RPMs, the RT engine is nowhere near as smooth as the ST11. That's what she felt. The ST11 can smoothly loaf along at 3500 rpm with that same load.
About that time I ran into a fellow with a 2009 ST1300 who wanted to sell it quickly. We made a deal, and as soon as I rode it the frist time, I knew it was superior to the RT. The power is smooth and endless. At first I thought the RT handled better, but after tweaking the suspension adjustments on the ST13, they are equal. The surprising thing is the stock ST13 suspension. The stock ST13 suspension is vastly superior to the RT, even compared to the RT with ESA. The ST feels more plush, but also more controlled. You can get good handling in the ESA firm suspension setting, but the ride there is not so good. Even in the ESA Comfort setting, the RT is no match for the ride comfort of the ST13. The vendor that BMW is currently using for shock absorbers, is simply not very good. I understand BMW is changing shock vendors for the 2011 model year. I hope so, for their sake. I have no doubt with a good suspension the RT would be great (my GS with Elka is superb), but as it comes from BMW, the suspension is just not competitive.
Of course there is just no comparison in the engine department. Both the ST11 and ST13 are superior to the R1200RT engine in every respect. Gas mileage is about the same for all three of them, so even that isn't a factor. I can get 50mpg if I'm easy on the gas with any of them, but of course rarely do so!
So, take it from a guy who spent the money for an RT intending for it to be the ultimate 2-up sport tourer. The ST13 is better in most respects, and the ST11 is not obsolete. The RT would be my third choice of the three. Reliability is not a factor in that comparison. I've owned several BMWs, and never had a problem with any of them.
The RT went to a new owner this evening. He has owned many BMWs. I'm sure he will be happy.
Don