A spreadbore that isn't modded may provide near the same or better as the modded non-spreadbore since the premise of the spreadbore is smaller venturi for better mileage and better driveability in cruise RPM's, then the big kick in the a$$ when you open up the back barrels. You could also make the primaries progressive on the 4 bbl your messing with, you may be giving up performance and other benefits without realizing it by blocking off the one barrel completely. Then you can delay how progressive it opens to tailor the engines needs even better. I think that would give you the best of both worlds.
