To expand on Vikki's comments, a lot of people over-carb when switching to a 4bbl. Then they lose low-end reponse. Stay conservative with the 4bbl size and you'll be very happy.

The deeper gear of the 2004-R will improve economy because you won't need your foot in it as much to get off the line (normal driving) and on the highway your revs drop significantly. Better off the line acceleration and fuel economy? Might want to reconsider your resistence to swapping trans.