A few comments...
There's a fairly big ergo difference b/w the F800ST and the GT, with the GT being significantly more relaxed. Also a longer swingarm, more passenger room, better luggage and 5 more hp.
This site is good for comparison, if you haven't seen it: http://cycle-ergo.com
As with most BMWs, there's a fair amount of aftermarket kit to change the ergonomics to your needs...bar risers, peg lowers, passenger peg lowers, seats, screens, etc. More choices than many other bikes, if that matters to you.
The belt drive is fantastic, and there are now Contitech belts (the original manufacturer) available on the aftermarket, mostly overseas. I just bought one for inventory, $113 delivered, as compared to $550 for the stock BMW part, which is identical. They are specified to be be changed at 24k, but usually last twice that or more...with ZERO maintenance, nada, nothing. I'd be hard pressed to go back to a chain on a travel bike. No drive line slop either.
The VFR is a great bike, I had a 1991 750, but the V4 is much more difficult to work on than the F800 motor, if that matters to you. 15 minute oil changes on the GT, nothing to remove, everything accessible. I've also come to love the under seat tank, easy to fill right to the brim, never have to remove a tank bag, always 50 mpg or more.
So...the downsides. The engine is "uninspiring" but very, very "competent" in the real world, with good torque, fueling and linear power delivery. The triple in the Tracer is more exciting, the VFR more exciting still. The F800 is a "relaxed" touring bike, 4k at 70 mph, just burbles along with that "twin cadence" you don't get with more cylinders. There's some heat that comes off the engine, primarily on the left side, more bothersome if you don't wear heavy riding gear. Great when it is chilly, less so when it is warm, not really an issue when it is truly hot b/c everything is hot.
The stock suspension is also only "OK" IMO, especially the rear shock, even if you get the ESA model. It is harsh on choppy pavement, which is kinda the entire US at the moment. I've got a Wilbers fully adjustable replacement on both of mine, made a world of difference, but not cheap.
FWIW, I personally will never buy a bike again without a test ride (been there, done that, sold it in a couple of months and took the hit). I was fortunate to rent an F800GT for a 10 day Scotland tour, so really got to know it. When I decided to ship a bike to Europe, went and found one. After riding it around for 3300 miles, came home and bought another, and sold my GS. No regrets.
Good luck with your shopping!