you dont need a turbo to make 600 with a 418.
Just to give you an idea, my 428 ran 8.89/158mph with 15 psi and that was lifitng off the gas near the 1000ft. I figure it to be some where near 850-900FWHP and thats with an 88mm .96 AR T6 that everyone tells me is to small for my set up.
Im not going to bother going to a bigger single, its twins from here on out for me.
1989 Mustang LX/Dart 428w/Turbonetics 88mm/AFR 225's/Solid Roller/Glide/FAST XFI -Nearing Retirement!
2011 FFR Type 65 Coupe (build in progress)- Dart 428Twin Turbo, Fast XFI, T56 - Just a street car!
2012 STI - Cobb stage 1 tune daily driver