caster for me is a big adjustment.
on one day, i had it neutral and was running .60s, switched to minimum caster and slowed to .90s, then switched to max caster and improved to .20s
as far as the weight transfer issue, i dont think so. heres why.
my buddy was running old mgs on his lo206 engine at 370lbs. he switched to new bridgestones and it was sliding all over. i asked him to try my tires so at the track we switched but he only switched the rears. he said there was so much grip in the back of the kart that it was pushing terribly. funny enough his lap times did NOT improve over the worn set so he also agrees that there is such a thing as too much grip.