I third the sentiments, except I like the ak40's quite a bit better than the ak50's.
To me MS is like a good middle relief pitcher. He's almost never the starter, but he might start in emergencies or in the right situation. Otherwise, you'll usually want to start your ace, which to me is the AK40's. That said, the middle reliever in the right situation sometimes might be the perfect selection...in this case stage lip for an instrumental band. I find the MS is great right there at the front because it gives you fantastic reproduction of the stereo image at that location. However, you don't have to move too far back before there's just too much side (room reverb) for my tastes. Sure, you can mix the side down to 30 percent or less in post to minimize the room reverb, but to me that kinda defeats the purpose of going MS. I've gotten some great stage lip recordings MS though, but only when there's no vocals because the vocals usually go around your recording since they're routed through the PA speakers. Bottom line is, if I only had one pair of Neumanns I had to settle on, I'd go with the cards/AK40's for versatility.