CL has aluminium panels so no rust. They do suffer corrosion where the c pillar meets the rear quarter.
Late 2003 onwards W220 doesn't rust.
The later cars also have the 7 speed gearbox which does help performance marginally but improves economy on a good run by a fair amount.
We've had pre and post facelift S500s and CL500s in the family. Post facelift is the only car to go with, lots of revisions, some you can see, some you can't.