I don't think you should give up on using skymiles on KAL. If they have a flight available BE is always 120K, not the phantom numbers of Delta. You may have to fly economy on the DL domestic end, but KAL TPAC flights in BE are a real value and even better if you can get on the 380 out of LAX or JFK, but the 777 flights from the US are all top of the line, but double check equipment on their website. Even if you can't use skymiles all the way to Chang Mai, as others have noted internal flights on Thai Airways are so cheap even BE is a great bargain. This use of skymiles is probably the most cost effective value skymiles offer using KAL aircraft. So don't be hesitent to use them on this flight.