Beef - this might not be what you want to here (as the Tiger is an awesome machine) but for what it's worth my advice would be get a GS. I had a Tiger 1050 in the UK and loved it, but as you say it's off road capability is very limited. I sold mine and bought a GS.
HOWEVER - you coud totally ignore this and just go with the tiger if thats what you like. As you sat Touretech do stuff for it and I'm sure there are people out there who've been around the world on a Tiger.
The new Tiger 800 is out this weekend so there is another option. However many peope will tell you NOT to undertake a big trip on a new model as it hasn't had time to iron out the issues. Again, who knows.
All I know is that you need to be happy riding the machine you have. Luckily for me I'm 16,000 miles and 3 months into my trip and I love my 1200GS. I'm sure I would have loved every minute on my tiger as well. - Not helping really am I
What I'm trying to say is any bike can work as long as you are happy and you know what it's capable of. If you're crossing Africa then I wouldn't suggest a Tiger but if your spending a eyar in South America for example then it would probably be fine. People have taken Haleys all over the world need i say more...
PS Whatever bike make sure you know a little about how it works and that you cna at least change the tyres.