I can't speak for the fees, rate etc you get in Korea but the key point is that when changing currency at Superrich (or the like, I just always use superrich as originally when we checked it was the best and is very convenient) there are no fees and you're getting very very close to market mid rate. So for example right now at Superrich in Siam Paragon the buy and sell rates for USD are 32.71 and 32.78 (at head office its 32.74 and 32.78). For all intents and purposes you're getting a free currency transfer. Looking at the Won the rates are currently .0294 and .0300 (Bills at least 5000 won, 1000 won bill a worse rate) so while the rate will change the amount of the spread shouldn't so you can use those rates and the rates/fees you pay in Korea to figure out whether you'd be better transferring through USD. To be honest, given how tight the speed is and the fact it introduces another layer of currency risk I wouldn't bother.