My impressions with these prior to testing them side by side have been that the M Plan produces slightly more contrasty and vivid results with less CA but that sharpness/definition were more or less the same.
The M Plan is 210/0 and the E Plan is 160/- so they were used at 200mm and 150mm extension respectively. Both are stacked from little over 100 exposures. Diffusion was a provided by a ping pong ball attached around the tip of the objective and the lighting was one Nikon SB-24 set to 1/16th power.
Test subject: crane fly wing
Left: E Plan, Right: M Plan
Compare them side by side with zoom/pan in flash HERE
I think this test confirms that the M Plan has the slight edge in contrast/punchyness and that if there is any difference in resolution it's not big enough to show clearly in 6MP images. This test subject (under this lighting) doesn't seem very revealing when it comes to CA so not much to say there other than both objectives can produce almost CA-free results under some circumstances.
The M Plan shows a significant drop in resolution along the right edge of the frame but not so on the left side as far as I can tell. Either my copy of this objective is not 100% or it's slightly decentered/tilted in my setup. In support of the latter explanation I noticed an image shift after changing objectives. I nudged the subject slightly to compensate for this but they still didn't end up perfectly aligned.
This is obviously very inconclusive but as I think I've mentioned before I prefer to gather my understanding from many inconclusive tests rather than trying to set up one final conclusive test (which IF it was possible (which I'm convinced it isn't) would take far too much time and energy)
***EDIT: Forgot to mention: click the images to download 6MP versions.
