Hi mate,
I can't comment on the DR or KLR, although I believe they're both good. I have a 2003 Yam XT600E though, so can comment on that!
I must say I've found it to be an awesome bike. It has plenty of power on normal and dirt roads, and enough for cruising fast enough, fully loaded on motorways. It's a solid, very reliable bike. It's relatively unsophisticated technology means that it is not only easier to fix for the owner but also for 3rd world mechanics, who won't be conversant with more advanced stuff. It will also (to quote Mr. Scott) "happily run on yak's piss".
I've crashed mine a couple of times, dropped it, run it on really rough roads fully loaded, and it just keeps going like it was born to that stuff.
There's also a decent amount of aftermarket kit available for it, including a 23 litre Acerbis tank which retails here for about £200.
You could do a lot worse than an XT.
Having said that, when I was buying the bike for my trip I just narrowed it down to 3 options (like you've done), in my case the XT, the BMW F650 and the Honda Transalp. I then went out with my money and an open mind and found that my best option for my money was a low mileage XT for sale in glasgow. It could easily have been one of the others. Assuming people with experience of the DR and the KLR confirm what I suspect, that they are also good bikes, I'd just go out and buy whichever one you can get the best deal on.
Matt

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*Disclaimer* - I am not saying my bike is better than your bike. I am not saying my way is better than your way. I am not mocking your religion/politics/other belief system. When reading my post imagine me sitting behind a frothing pint of ale, smiling and offering you a bag of peanuts. This is the sentiment in which my post is made. Please accept it as such!