I've tried many. I kept: Nikkor 85/2, Summicron 90/2 v3, Summilux 75/1.4, Hexanon 90/2.8. The Hexanon is a copy of the G-Sonnar 90/2.8 and identical in size to the Elmarit-M; in practice I didn't find much difference in using the two lenses.
In terms of rendering, most similar to your 50/1.4 are the above 90/2 and 75/1.4 (all three lenses designed by Mandler).
All 4 lenses above are outstanding and I can recommend each, depending on your budget/size/speed requirements. Have a look at the flickr M-mount forum, see what people do with the different lenses. I recommend to decide on signature, not on resolution, APO/ASPH, etc... the performance of a tele on an M is mostly limited by you, not the glass (focus accuracy, etc.).