Also, can someone verify that the lowest pre flop hand that can be the stone cold nuts on the flop is indeed 26s and not any of the other answers given?
We need to flop a straight flush for the stone cold nuts, as quads on the flop is vulnerable (to higher quads or a straight flush). We can't have the ace on the flop, as then we are vulnerable to a runner runner royal.

23s cant make the nut straight flush without an A on the flop.
24s is vulnerable on a 356s flop
25s is vulnerable on a 346s flop
26s - flop 345s no higher straight flush is possible (as we hold the 6)