I'm running a single s 475 and like it right now and have a hx 40 sitting on the self and thoght about using them for twins but don't want to hurt the trucks hp.
I am running a super hx40 over a s475 and I really like them. Spoolup is decent and they supported over 600 hp without egts going wild. I run this setup with Mach 2's at 470hp daily and tow heavy with no issues at all. If the price is right i wouldn't pass them up.
Joe