I owned an LS-3 for 13 years. In my experience, all LS-3 versions
climbed equally well but many (not all) A models didn't run as well.
The lower weight of the 3A should have had some impact on climb but I
never saw it. The most likely cause of the cruise discrepancy is wing
profile, for two potential reasons. First, as you note, is that the A
model airfoils may have been thicker than they should have been (per
Dick Johnson and some correspondence in Soaring mag. from the factory
that followed Dick's test). Second, at least for the 3, is shrinkage
over the spar caps that caused a flat spot to develop after a few
years with significant impact on cruise performance. I contoured my
wings twice and profiled them over the spar caps once (to build up
this flat spot) and my glider was equal to the ASW 20s, Ventus, and
LS-6. A few other pilots who did similar things had the same
experience (e.g., Jim Cox in TX, IIRC). Unmodified LS-3As fell away
pretty fast at higher speeds, but so did unmodified 3s.

The above covers why a 3 might perform better than a 3A. Another
factor that relates only to how a 3 or 3A might perform against other
types is that the leading edge of the wing was said to be too blunt,
especially on the outer wing. The aforementioned Jim Cox profiled his
entire wing and built up the leading edge to the correct profile and
saw a dramatic improvement. But as far as I know, both models of LS-3
had this characteristic.

Personally, I'd probably take an LS-3 over an LS-3A even though the
wing is heavier--the 3 has fully automatic controls whereas the 3A
requires some control connections--but I suspect that either glider
would perform very well with the proper wing profile. They're still
very nice, very strong gliders. It's not well known that when the LS-3
and ASW 20 first appeared here in the US around 1977, the '3 was the
hot ship to have.

Chip Bearden
ASW 24 "JB"
New Jersey, USA