Hi Ronnie, Please accept my apologies for an unfortunate snap crackle pop answer to your question regarding weight / use of chrome / black Leica lenses. During my 53 year career as a working photojournalist, weight consideration one lens to another has never been a subject of interest nor consideration.
In my case where I work 99.9% of the time with available light only, the most important aspect of a lens has always been ... "how fast is it?" Not it's weight nor how long it would last. After all it's always been considered, by my self, buying Leica was buying the best. So longevity of use, chrome or black, was of no concern as it was assumed the cameras and lenses would out live me anyway.
I've always worked with 3 M's at a time, presently M7 with Tom Abrahamsson RapidWinder's attached, obviously with different lenses, as changing a lens always left the possibility of missing a picture moment while changing. And on a fast moving assignment even with 3 cameras at ones finger tips a picture can still be missed.;-)
In my many years I've never heard of any discrepancies chrome to black during use and the only preference one to the other that I re-call, has been for the "look of chrome to black or vise verse." Some folks like pretty and there's those of us who prefer black for functionality and looking cheaper, like black point & shoots!
And as I've always used black since they were available because they don't look like priceless shining jewels hanging off my neck and not to draw attention to myself where I'm trying to be absolutely discreet as possible.
I trust this is an acceptable answer for you and once again I offer my apology. ted
"DOCTORS' WORK" book
http://www.islandnet.com/~tedgrant/ Ted Grant Photography Limited
S&les from "Women in Medicine" book project
http://www.sandycarterphotography.com/WomenInMedicine.htm