I have had big Newts. I have a 12 inch now. Their performance is lacking on the close, unequal doubles I like most to view and challenge myself with. It's probably a combination of central obstruction, fast focal ratio, and spider vanes. A slow, unobstructed reflector design might work, but it would be as long, and might be nearly as costly as the equivalent apo, if the optics are custom made by an expert mirror maker.
A big Newt has worked ok for me on the unequal ones that have wider spacing, like Xi Peg, or the very tight equal doubles. They fail on double stars like 90 Herculis, at least in my experience.
I haven't tried 90 Herculis but it looks very doable to me. When I'm back in San Diego along the coast where the seeing can be very good, I'll give it a try.
I think the biggest issue with a Newtonian is thermal. To split the tough unequal doubles, besides the good seeing, it takes real time to reach rock solid thermal stability even with aggressive ventilation.