Yesterday the SO and I went the dealership so she could test ride the F800GT. She rides an R1100S now, that I've fitted with all the possible farkles from screens to barbacks and gps to lights to make it into a suitable touring bike for her. The dealership also provided me a used F800ST to accompany her (my K1200GT was in service for a look at a couple things). We rode a mix of urban, some curves and some interstate at speeds fast enough to get a good run and switched bikes.

Some comments
Despite published numbers, any possible difference between the ST and GT in usable power is tiny, if it exists at all. Neither of us noticed any real difference.
The GT was a brand new bike and its motor reminded me of a new RT motor prior to break in- some thudding from tightness in the way it ran. The used ST motor was butter smooth- got no idea what that vibration is folks grumble about on the 800- neither of us felt any on the ST- though in fairness her 1100 is not the smoothest bike on the planet so she is used to some vibes. The service guys say the GT should break in to be as smooth as the ST and I can't see any reason it would not- they're pretty similar metal.

Re ergos, the (stock) ST was pretty obnoxious for both of us. She said she felt like she was perched on top and I felt like my knees were in my nose (6 ft with 30" inseam, about 175 lbs). The GT is a whole lot better but while fine as a summer fun toy as is, its not all season touring ready from the factory and needs ALL of the usual add ons. Specifically, pegs are still too high despite their touting them as lower. Lower yes, but not low enough. She might get by- I would surely need them lowered or the seat raised or both. A taller screen and barbacks are needed, the latter requiring a brake line change. The existing bar location is OK with the stock screen for summer play but not for all season touring - as usual for BMW bikes it is a bit much of a forward lean- but no where as much as the ST. The stock seat is a bit soft but may be OK if you're light- there are all the usual options and they're worth evaluating before purchase.

Re the power, both bikes are adequately responsive and powerful enough for any normal use including hard play in twisties where the lighter weight of these might make the GT a premier twisties play choice for a touring machine (though not in the class of a true sport bike or supermoto). I know I would enjoy riding one of these in the NC mountains as is for a while and longer if the ergos were corrected. The GT handles light and flicks well- easier than her R1100S- and much easier than my RT, K-GT, etc. The fuel below the seat no doubt helps that feel- the GT feels light in all modes. The belt drive was smooth as expected. The ST's broken in tranny was super smooth and positive and the new GT only slightly less so- should be the same with a few thousand miles. I like the smooth shift into first from upper gears, unlike the trannies on my BMWs that need some careful moves to get smoothly into first on the move.

She's 5' 5"plus a bit and was comfortable with the height of the stock bike, also commenting that the light feel would make it easier to do tight U turns with confidence.

Didn't look at the stock tires but they worked well whatever they were- didn't feel like the crappy Bridgestone 020s that came with my RT. The brakes on the GT are outstanding- powerful with a light controllable feel- among the very best I think.

Re the safety and luxury packages, I suspect most bikes here will have both but personally I could pass on the safety package. Got no real need or desire for ASC (really, do you need this stuff on a bike this light and well coupled) or tpms etc
The luxury package is a must have for serious use- got the heated grips and other stuff in it. The ESA on the GT does little but doesn't cost as much as on the other bikes either- I'd rather dump it for first class shocks though I'll say the stock shocks on the new bike were pretty decent for stock stuff. We both thought the ride comfort of the GT was good but of course would need a 500 mile day to fully evaluate.

All in all, we both like the F800GT a lot but given the price and probable depreciation its a tougher call than an R bike would be. She's thinking on it a while.
I'm checking into the needed farkles.

If you're at a stage where you're hunting a lighter bike or if you're a female rider or if you vertically challenged, I'd suggest you go ride one at your local dealer. It may very well be exactly what you want, especially with whatever farkles you need to make it fit you exactly. I'll predict that most of us would be faster in any tight curves on this bike than a heavier R or K bike due to its sweet combo of handling and power to weight.

No it does not have a cruise control. I don't care and she's never had one on any of her stuff. But this omission is a screwup in terms of attracting riders from other BMW bikes. The older riders who want to move lighter from an RT will expect it to have one.

On this size bike I'm not sure I'd want the top case. Probably just side cases with a good waterproof duffel for the hotel room. And it comes in 2 visible colors unlike some other models- white and a muted orange, plus the usual drab whatever.