[Leica] Yet another 50mm lens question

[summicron at bellsouth.net (Frank F. Farmer)]

Greetings,

I am in the midst of purchasing my first 50mm lens to mount on my M3.  I 
know that this list has had a pretty good discussion of 50's in general of 
the past couple of days and I do not want to rehash anything.  However, I 
have a more specific question about a used lens that was not really 
discussed as far as I know.  In particular - from folks who have used this 
lens - what do you think about the early - mid seventies 50 Summicron?  I 
believe I'm referring to the 4th version without the focusing tab or the 
"50" on the barrel.  

Stephen Gandy's site has this to say:  "Fourth version 1969-1979 Black lens 
with no '50' on barrel,  No  focusing lock or lever.  Generally reputed to 
be a notch below either of the Summicron versions before or after it. 6 
elements."

Why was it generally reputed to be lower performer?  What does this mean in 
practice vs. in the lab, if anything?

Have those who have used both the 4th version and others found it to be a 
"notch below" the others?  Any comments, experience or wisdom would be 
appreciated on this topic.  

As always, thanks in advance.

Frank Farmer