Hmmm, I think the answer to the question is another question or two.
So are we talking prints or slides? Do you use a tripod all the time? Have you a colour meter and a set of balancing filters?
If prints then what size and will you do everything yourself the old fashioned way or go to a lab? My experience is that even slides vary slightly, more than the lens does. But no one has mentioned colour meters or whatever you measure the whites with, nor correction filters etc: this brings in a variable. So does the lenses & bulb in the projector and the screen...
As for prints, talk to people in labs and they'll usually say (well, mine do) that they print thousands of 4 x 6 (sigh), nowhere near as many 5x7 and a few a bit bigger. Get seriously big and you'll notice the difference. But the difference I notice is who printed them. I can always pick out the technician sitting at the machine by looking at the prints.
Others have said that the differences in normal prints at normal apertures are non existent and I'll go along with them. And I can equal the M2's output with my wife's elderly 3 megapixel P&S. Even B&W up to about A5 size.
Personally, I wouldn't worry about it. From about 1945 or so when coatings appeared they've all been better than most people will ever need.
You should also be thinking about a set of lenses (very expensive) and not just one.
The only ones with signatures I notice are the 30's ones like the Summar and the 9cm & 3,5cm Elmars. All the rest from the uncoated Summitar onwards are just plain old fashioned good.
BTW, by the time the photo has gone from a negative to a scanned print and then the print is scanned and loaded on to a website - where more software deals with it - it is far from pure and is very third or forth generation. So it's not the place to look for signatures.
Sorry, I seem to have ranted on more than usual. I'll go and lie down for a while.
Regards, David