Jerome Conners wrote:
What glider will provide the best characteristics for
mountain wave ascents to record heights?

What are those characteristics...air foil design, lofting
characteristics, L/D ratio, oxygen system, etc.

Jerome Conners, PE

I really think that a nice high Vne would be great,
since during a record attempt one would want wicked
winds aloft (120+ knots on the nose) and it would be
terrifying to choose between exceeding Vne/flutter
speed or drift downwind uncontrollably.

Sounds like a Jantar might be a real solid choice
Apparently without water ballast which might freeze...
Maybe an LS-4? I'm considering these factors myself...