TonyS6 - if you're flying 4 times a year overseas, and you do about 50,000 miles a year, I'm guessing those 4 flights are pretty much all the flying you do or maybe a couple of domestic trips in addition.

If you are buying Biz class tickets for those 4 trips, DL would be a good airline for you since the BizE product they have is nicer than business on the other domestic carriers, and those 4 trips would get you to Platinum or very close to it.

If you're upgrading to Biz, forget about it on DL since you would have to use miles and availability is sketchy.