"That thing gotta 273?"

When someone has not run the different motors, and wants to do math exercises, things are not linear nor the same. I had a 71 340, 4 speed Duster. It was fast, and I still have the 340 and 2 others, as a backup if the 273 ever fails. But if you set any small block up with the same heads, intake and carb, they will run very much the same. The peak rpm drops as the engine gets larger. The limiting factor is the "safe" rpm. about 7,000 rpm with a good small block bottom end.