Ryk wrote:
I'm about to add a spin rig on my Hughes 35 (I=44ft, J=14.5ft). A
little googling yields a variety of opinions on the reasonable upper
size limit for an end-for-end gybe. I think the boat is too big to
manage it with single, loaded sheets, but that it should be manageable
with separate sheets and guys.

You seem to be equating "single sheets" with "end for end". Doesn't
have to be that way. I once sailed on a NY-36 which did end-for-end
gybes with separate sheets and guys.