In some ways the new KLR and X-Challenge are world's apart. As Yuma Simon sez...much depends on your plan and the what, where and how of your trip.
Your riding experience could factor in too.
Since your in Aussie you have lots of bike choices. The main difference in the BMW and KLR is Price! In the USA the KLR is half the price of the BMW. Typical. So is the BMW $5000 ($USD$) better than the KLR? Depends how you look at it and what you want to do.
Now add up all those TourTech items the Xchallenge will need. Figure "about" $1400 US to outfit a KLR in luxury form covering most ALL it's faults and equipping for RTW travel. The Beemer will be more $$$$ I would guess.
I owned a klR years ago, didn't much care for it, really uninspiring and needs quite a lot of mods to be OK. Rode it through Baja and mainland Mexico, put 5500 miles on it in 6 weeks riding. Turned it back in the minute I got home. Nothing wrong with the bike at all, just not my style.
The '08 is better in most every way. I just rode one (my first short ride on one!!!) this past weekend! Everything is better than the original KLR. But still, it is rather uninpiring compared to the competition....For BMW money I would look carefully at the KTM 690 Dual Sport bike. Also look at the DR650, a very popular bike in Aus, no? The Honda XR-650-L , XT660 Yam...they are all worth a look and a test ride.
As an RTW bike the klR is not a bad choice at all. We don't get Yam's in the uSA, so after the DR650 (my current mount) the NEW KLR would be my 2nd choice in a single.
The KLR is a tool, pure and simple. Cheap, expendable, mostly reliable, tough and can be loaded up nicely. The F650's (either Dakar or GS 650's) would both be better travel bikes IMO than the XChallenge. The F650's have proven good on the road, but not without problems, still a very popular bike, a known commodity. Among US RTW riders the KLR is perhaps THE number one choice.
At the HU meetings you see A LOT of KLR's.
The Xchallenge is an unknown at this point as a long term distance bike. I have NOT ridden it, but did test out the sort of Super moto brother (forgot designation).
It was fast! and nice on the road. But all three of these new BMW's look a bit spindley for hauling gear over rough terrain. Dunno. Jury is out. Same with the motor. How will it do? It's only been out just about a year and a half. I would not want to be an unpaid Beta tester for BMW. I'm sure there are owner web sites where much new info could be learned. Go there, do your homework.
Patrick