If you've changed CVT fluid 6x at this point (every 20K miles), I'd think you're good as-is. 6x better than most.
I agree. Contaminates and wear metals drain out with the old fluid. Using fresh fluid is always a plus. I am not sure straying too far from the OEM fluid spec is required or helpful. Nor do I believe there will be much difference between brands that make compatible fluids. I think it would simply be a guess at this point. CVT's have some very interesting operational conditions. Honda's CVT is different than Nissan's and has a different fluid requirement. I don't think Redline's fluid is the right choice.