A very personal choice to make. I'd recommend you borrow an F800 for a few days first at the minimum.
I sold my 2004 1150GSA and got an 09 F800 in June of last year. I'd toured on my 1150 for a couple of weeks around France, Italy and Switzerland. Bike never missed a beat and was all-day comfortable (low seat too). However, as a solo traveller, I was concerned at the weight and I was aware that If I dropped it on an incline, I'd need help to get it back up so that I could get the sidestand down and get back on it. I'm 5'9" you see .... I was also looking wistfully at some serious off-roading on narrow tracks but couldn't do it as if I came to a dead end or needed to turn around, I'd be stuffed. Not saying others would be - just that I would.
Also, getting it out of my garage and up the ramp leading out from it far enough to get the garage door down was a hernia risking move
I took the plunge with the F800 and haven't looked back since. Wife and I tour 2-up and it definately isn't as good as the 1150 for long motorway days. The bigger motor obviously works a little less hard and the F800 one is a bit more revvy. But then we don't do those often enough to make having the bigger bike and suffering the other 99% of the time worth it. For days out and A and smaller roads it is fantastic solo and 2-up. It does cope fine 2-up on motorways at or the legal speeds and up to 85 too but that's not where it is happiest. I also go off-road with much more confidence than I ever did with the 1150.
Think about what you do most of the time on your bike and get a bike that does that better than what you do least on it. Unless you feel the need for 'road presence' or other more subjective criteria.
There are plenty of bikes that can do what the F800 does. Some better on road and others off-road, but for me the F800 is a good all-rounder and for anyone wants a good upright riding position and decent economy on a go anywhere bike, it as as good a choice as any. Even the low seat can be gotten used to

I'm sure there are people here who could easily outride me on and off road on an 1150 or 1200 with me on my F800 but that's why it is a personal choice based on many things.
The biggest differences are weight and fuel economy.