I've owned the 40 SC and 35 MC, though not simultaneously. The 40 gave a more modern rendering, had less barrel distortion, and was (dare I say) a bit sharper. The 35 was designed specifically to emulate a classic lens, and it added more "character" to my shots. Focus shift on the 40 is noticeably less than the 35, too. Bokeh was a perhaps a touch less harsh on the 35. I couldn't tell the difference between SC/MC in actual use.
The 5mm FL difference WAS a big deal to me when using 35mm framelines. I tried the 40 as a cheap and compact one-lens solution, but the framing inaccuracy really got to me. The 35 was a lot of fun, but its idiosyncrasies and I began favoring a 28/50 combo anyways. Lately I came back to 35mm but with the f1.2 beast... truly a legendary lens.