Hi there,
My lab routinely uses SSCP. We find that both at RT and in the
cold room if you run a 6% gel in 0.5xTBE at 70v overnight you get very
good sensitivity for a 270bp fragment. You say you are worried that
sensitivity will decrease if you run it longer. I would say that running
it for a few hours at RT would be a lot less sensitive due to the
temperature of the gel at that sort of voltage.
hope this helps
cheers
Nick