Andrew
As you were - an 1150 GS will do you fine. A 1200GS may well do it better, but it's too early to say. It's a bit lighter, but I can't see that making a massive difference to cross-wind stability.
If you can afford it (£9,300), can wait till March and like the looks, get an order for the newbie in now. If you want to spend less and want something sooner, the 1150 will do you proud.
I rode mine down to Italy last summer and did a couple of 600 mile days in relative comfort - cruising quite happily at 80-90mph with occasional stints at a ton plus.
It really was fantastic for that sort of thing, and as you say, it'll do the town thing as well.
Do it.
Phil (6X)