Originally Posted by NCommander

It should be noted for the record that M fares are extremely expense, and I find business on Delta not to be worth the price of admission, though YMMV. If your booking more than 50 days out, an I business class fare usually should come out close or lower than an M fare.

EDIT: To above poster: I thought you could only upgrade on DL operated flights?, I do know under some cases you can upgrade KL or AF using with a SWU, but not with miles. (granted, this info may be out of date ...)