Noel,
First of all, I have owned a grand total of one glider(DG303) and
done one contest, so I may not be the greybeard you want to hear
from! If you are planning on flying in sports class, the DG300 has
the better handicap(at least for OLC, 106 vs. 108), so if you fly even
with an LS3 you will win the day.
The responses on the thread have indicated years of experience and
multiple glider ownership. My gut feeling, from observing pilots and
gliders on fun days and contest days, is that you and I would
probably have to move up to ASW27 or comparable to get to the next
level in performance. Just fly the heck out of your DG300 until then
and have fun. I really feel it comes down to experience and comfort
level in varying conditions and terrain rather than equipment unless
you are at the top level.
Is it possible that I got a letter from you when you were searching
for a DG300/303?
Good luck in your quest, and I echo some other posters here
regarding the auto hookup on the LS3 elevator. And I concur with you,
loved the LS4, almost bought one!

Dean "GO"