If your bike is later than 02 then Triumph stiffened the suspension and made this into a touring bike, previously it had softer springs and was better offroad. Reliability is not great on these, I have had 5 Triumphs and all let me down and I was chatting with a guy who toured on an 04 on heavy fire roads and had to be rescued by a Caponord which might be the biggest insult I can imagine.
The fuel pump fittings on earlier bikes were plastic and guaranteed to break, at one point alloy fittings were available for a free upgrade but otherwise they run to about £30. Well worth fitting them. The cable connectors were needlessly complicated and can separate just from vibration. There are various other common flaws but check out the Triumph forums for more info and just check yours out.
My overall opinion is that it's as comfortable as a BMW R1200gs but not as good (handling, usefulness offroad, torque, build quality). It's about equally reliable though.
I have had 4 BMWs and reliabilty and quality is a serious issue with them. I would say I am larger and heavier than you and currently ride a 650 single for long range touring. I have gone for reliability over the extra performance but there are times when i miss the extra power. I would steer clear of the F800gs. I had 2, both had a host of problems, none of which would have stopped it running and all were warranty issues but it shook my faith in the bike. My brother had one, same issues. Also the seat is very uncomfortable after about 50 miles but the ride is good, it's good offroad and the economy (and therefore range) is top notch. It's a great bike flawed by some irritating quality control issues and cut corners in production.
As commented earlier, I am also a big fan of BMW singles. I have the G650 X-country now and it's been a top performer. It does feel a little small but it's very reliable and cheap to run. It has flaws so factor in extra costs in getting it trip ready. If I didn't have this I would be looking at a Dakar right now but although it's very comfortable you might find it a bit breathless after a Tiger, it's not as powerful.
As I said, I had a Tiger but it let me down within the first 2 weeks so I got rid and bit the bullet, bought myself a 1200gs. That is a great bike but it's not reliable. In the end I gave up on "nice bikes" and bought a small, functional, reliable and usable machine. Others in the class, if you're thinking offroad are the KLR 650 (reliable, old fashioned, easy to maintain, slow, tricky to get upgrades for in the UK), Yamaha Tenere 660 (good, over-priced, slightly heavy for power but easy to tune). I have a soft spot for singles, I have had dozens of them and of all the kinds of bikes I've had they are the least troublesome and around lanes and twisties they still tend to be good fun.
Sorry... I ramble...