“Best” all around axle ratio: ~450hp w/ A904?

Obviously 3.55s or 3.23s are the choice, and with a 408 and a decent stall converter, I think either will work for you.
If you want to retain the 26"tires, I would go with the 3.23. If you are open to a 28"tire, (and can fit them) then I would go to the 3.55s. If you have the 3.55s and want more go, you can use 26s. 3.55s and 28s are almost a tradeoff with 3.23s and 26s.
My choice? 3.23s, 28" tires, and a custom 3200 converter.....