I just got done doing one year in the ROK. I was stationed at Osan AB. Where will you be stationed?
Once you figure out the roads, and where to go, you'll find Korea offers some of the best riding anywhere. There are tons of beautiful mountains over there and few straight roads. You will not regret making the effort to bring a bike with you.
As for which bike.... When I went I had the choice of bringing a DR650SE, a BMW R1200RT, and a VSTROM DL1000. I opted to bring the bullet proof and versatile VSTROM. It proved to be a great bike for the mix of city and open country riding. And it is as reliable as a hammer.
I did have one mx issue with the Strom (it was pushing 35k when i brought it over), and finding Vstrom specific parts/service was a little tough. Ordering parts on-line and sent to an APO box was easy enough. There are plenty of excellent mechanics in the country, and they will work hard for you, at reasonable rates, even if they've never worked on your brand bike before.
I only saw one other VSTROM in Korea the whole time I was there. I saw a ton of harleys and BMWs, and there are good dealerships for those bikes all over the country. Jap bikes seem less popular over there. Might be some lingering ill-will from WWII, but I think Koreans are very brand concious as well.
Given your list of bikes, if you trust and enjoy riding your Buell, that would probably be a fine bike to bring.
'07 R1200RT, '06 VFR800A, '08 SV650SFA, '05 CRF250X
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