Try the search - there is a LOT of good information on here!
Many people have been successful in redeeming the SWUs on DL, AF, and KL...
The gist:
AF Y+ fares are reaosnable - south of $2k - and avsailability for "O" class, upgraded or award busienss is relatively good - far out or really clsoe to the flight
Not so sure about KL
DL - people moan and groan about the YBM decision of DL, but this is the fact of life. With advanced planning, like your exeprience probably, you can get cheaper discounted J fares with a confirmed seat. M+ fares, available clsoer to departure, would run you over 2K...
A new benefit is that you can standby with the SWU on DL on the day of departure, if booked in an eligible fare. Thus, even if no Z inventory shows up ahead of the flight, you sitll have the chance of getting a seat at the gate. Risky busienss and you'd be out a lot of money if you don't...
I guess that's basically it