Don's 3betting range against a super-nit is carefully selected for bluff value (blockers) and post-flop play value (in the event villain calls). So long as villain is folding enough, then we don't need a great deal of equity post flop, if indeed we need any at all. But if villain does call, we know we're way behind his range, so we want hands that are capable of making the nuts, while also making him a big hand. If we have JQs and flop the nut straight in a 3bet pot against this nit, he's very likely to have a big piece of this flop too. Primarily, we want him to fold, but we want to increase our ev in the evnt he continues.

My only worry is that we're not going to get a 6/4 to fold to a 3bet very often at all, since he's already only raising very strong hands, so personally I'd be folding most of my hands to a 6/4 raise.