Margus is right, the mag wheels are more pavement oriented. Think Suzuki V-Strom, or super moto.
For bad road rtw I think that spoke wheels are better, BUT will require more maintenance and are heavier iirc.
MOST people will be fine with mag wheels on a rtw trip. MOST people do very little serious off-road that would be a real problem for mags, especially on something the size and weight of an RxxxxGS. IF you go for mag wheels, just go a little slower on the rougher roads, take it easier. 99% of the time you're on pavement and it doesn't matter.
Remember that if you do bend a spoke rim, you will probably end up replacing the whole wheel anyway. Yes, "spoked wheels can be trued", but these spoke wheels are so hard to true that BMW says it can't be done and recommends replacing the wheel. (It CAN be done but is difficult and expensive - it is NOT something your average mechanic is going to have a lot of success with, especially if it's dented)
If you're a very good rider and want to visit all the bizarre off-pavement little places in the middle of nowhere, then spoked wheels are the way to go.
ymmv...
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Grant Johnson
Seek, and ye shall find.
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One world, Two wheels.
www.HorizonsUnlimited.com