4k vs 5k Cams (Small valve [38mm?] vs big valve [40mm])

[The Quattro King]

I am in the middle of changing out the head on the 84 4ksq.  I am replacing
it with a head from a car (I think it was an 88 5k) that had the bigger
valves.  Here is my Q:  Although I can't measure (did not use a micrometer)
or see a difference in the cam lobes, is there any difference in the cams
from these two heads, side of the reduced surface area opposite the cam
lobes?  Why is the surface area reduced opposite each lobe?  Is this to
rotate the lifter?  Reduce friction?  Reduce rotating mass?  Is there a
preferred cam?  BTW, the teeth for the distributor gear are the same on both
too.

TIA  

Shayne P.



1972 MB 280 SEL
1984 4ksq
1987 4ks
1991 v8q5
1991 200q Sedan
1992 S4

Parting:  1972 Mercedes Benz 280 SE 4.5