50mm on the M8 is 65mm, 1.3x crop factor. 35mm is 45mm.
I am using a 50mm on my crop 1D body, as well as 50mm on my RF bodies. I also have a film EF body that I use from time to time, no 5D yet.
Honestly there is only a slight difference, no need to change your entire lens setup just because of the crop factor. Just learn to shoot with a tighter angle.
Personally I was also planning to get an M8, but decided to save up for a 5D first.