Mike, Hope you have decent sample that has the accurate RF coupling (important).
You guys have got to stop talking up this lens, or prices will go up
again. Back when prevailing "wisdom" was that they were mushy, unusable doorstops, they were fairly reasonable in price. (The fact that they had a special breech mount that only fit the Canon 7/7s helped. So many seem to be going to M-mount conversion now that I expect the unconverted ones eventually will become rare collector's items.)
Now they seem to be enjoying a second life on digital cameras -- thanks, I suspect, to the fact that a bit of unsharp masking cleans up the mush very nicely, without sacrificing the lens' unusual "signature."
About the RF coupling, yes, it's extremely important; focusing accuracy is critical, as you might expect. And you can't just assume it will be correct; based on my reading of the Canon 7/7s repair manual, I believe that Canon calibrated its RF lenses based on slightly different assumptions about film flatness than the assumptions Leica used. That means a lens that focused perfectly on a 7/7s may not focus perfectly on a non-Canon body, unless checked and adjusted. If you're having one converted, the converter can do the compensation; if you've got an already-converted one that's a bit "off," a good optical mechanic can zero it in by adjusting the "collimation shim," a precision brass spacer (hand-selected for each individual lens during production) that determines the depth at which the optical head sits in the focusing mount.
I know I've linked to these in other threads, but as long as we're on the subject, here are a couple of my own 50/0.95 picture batches: one from back during my "film era" (on a Canon 7s) and the more recent set on an R-D 1:
(This second batch will show you why Vivek says a lens hood is so important!)
It wouldn't surprise me if a Noctilux were at least somewhat better, especially in terms of contrast and flare control. But I use the Canon for its "look"... and besides, there are many, many dollars standing between me and ever owning a Noctilux, whereas the Canon is reasonably accessible.