1- LT heavier at parking lot speeds, you will get used to it, I am one of the guys in this Forum that just cannot understand the issue people have handling it at slow speeds, never had it down, could do a full circle (6 feet diameter) with the bike no problem so yes it is 300 lbs more but you have to get used to what is under you. What I like to say is: "You will handle the RT at slow speeds, THE LT will TRY HANDLE YOU. Just DON"T LET HER.... LOL
I'll add my own thoughts to yours if I may. I own both an LT and an RT.
I have no problems handling the LT at slow speeds either. Don't let the idea of it's size/weight intimidate you. Once your used to it you shouldn't have any real problems. I can't claim to be able to do a 6 ft circle, but I can at least turn it around in the road.
2- Traveling super slab all day, LT has a 4 cylinder and IS with NO DOUBT a smoother bike. With the RT vibes will make your feet and hands numb after a while, (Boxer Buzz) Throttlemeister will fix the issue on the hands, not feet, again the 1200RT is supposed to be much better on that department, much smoother.
You WILL like the smoother ride of the K engine vs the boxer. I find the seating position on the LT to be more comfortable too. The LT is THE suberb interstate travelin motorcycle
3- Wife, well unless your wife is a total stick figure person that will be confortable on the back of a CBR 600RR, the LT is the winner, she will love the seat more than any other bike. My wife loved it, but said the fact that the RT seats is thinner (so to speak) she had more leg room, on the LT the seat is soo wide that leg room becomes very little, the BMW adjustable passenger footpegs is supposed to fix that.
The rear seat settled it for my wife. I bought her some adjustable footboards since she's on the short side, but it was the seat that decided it for her. She's done up to a thousand mile day with no complaint.
About the seat anyway.
4- Solo riding in the twisties, as far as I am concerned, weighting out the fact that the LT is 300lbs heavier still they both handle perfectly, yes the RT is lighter and more flickable but again as mentioned before for 300lbs more the LT handles just fine. With two up on the twisties my LT always scraped the center stand, my RT never scraped a thing.
True, the RT will handle the twisties better than an LT. The LT's size doesn't take anything away from it's being a fun bike on curvy roads though. Think of it maybe as a PT boat compared to a cigarette hull.
Finnaly I am a water cooled bike guy. Bumper to Bumper traffic, if you ever get stuck in it, will cook the RT, your legs, fairings you name it.
I'm generally and air-cooled guy, but I gotta admit, I do find that same advantage to a water cooled bike.
If you have a spouse/sig. other, in all around terms of two-up comfort the LT is your machine. It'll really depend on the kind of riding you'll be doing most. I bought the LT for long distance and two-up riding and the more manuverable RT for local in-town solo riding.
This is a great site for LT info. For more RT specific info, check out www.bmwsporttouring.com