What should I expect from 450hp?

273 said
3.23 with a 408 is similar torque to the ground to a 3.55 geared 360, basically a 408 allows you to run one gear step higher than you would with a similar 360.

or about two steps with a 340, does it pull as hard as your 340 with 3.73 gears?

I’d say so, it was a 380hp 340 so ran pretty good with the 3:73’s