KGV class were rated at 28knots but could be forced to 29.25knots, while Scharnhorst could manage over 31 knots if forced. It did reach 31.65 during trails but those are usually at standard displacement.
So the advantage would be at most 2 knots.
BTW at DS the seas were 'moderate' swell according to O'Hara.
S&G were badly overweight and consequently had very low freeboard (~6ft less than the KGV's).
Are you sure about that?
Anson at 46,000 metric tons had 5.6m freeboard at stern and 5.2m freeboard amid ship with 7.44m freeboard at bow. That's an average of about 6.08m free board .
Scharnhorst had depth of 15.6m stern 14m amid ship and 17m bow. Max draft at 38,700tons was 9.9m, while standard draft would have been about 8.3m. So normal draft should be 9.1m.
Thus at max displacement the Scharnhorst free board should be [5.7+4.1+ 7.1m] /3 = average of 5.6m free board. At Normal displacement this average should be 6.4m.
doesn't look like 6 feet.