I really like the clarity of the AK50s but to me they sound thin out of the box. I never liked the raw recordings I made. I've had several people send me recordings that they absolutely love but I always find the lack of LF bothers my ears. The roll off is especially obvious on my home playback system where I can reproduce some deep bass. In the car it doesn't seem as severe.
A friend who loves the 50s suggested two things to me: (1) learn the pattern graph and use the off axis response curve to bring the HF more inline with the LF roll-off and (2) apply an EQ curve in post to correct for the low end roll-off.
I tried (1) with improved results but I have not tried (2). After I transfer all my old masters again, I'll probably try the inverted AK50 response curve to see if that changes my mind.
IMO the MK41s are the best hypers for the section. If you plan to keep additional capsules in your bag, then I'd stay with the Neumann AK40 or AK43 for running up front and EQ the AK50s in post. I've heard some great FOB tapes with MK41s but they never ripped my head off like some of the FOB AK43 tapes I made. If its possible to keep the 140s and also have the MK41s, I'd do that, clamp the MK41s in the section and then head up front with the AK40s.
(ned posted while I was typing. We were just discussing this topic a few nights ago.)