weight definitely seems like as much or more of a factor than width. i went from the stock v6 wheels/tires to gt wheels/tires. could easily tell weight difference by simply picking them up. only 225 to 235, but the added weight meant about 2-3 less mpg. i get 23-24 now in 50/50 mixed driving. can flirt with 30 going 60 mph.
2013 V6 MT Sterling Grey - 3.31 gears, JLT Intake, Boss Strut Brace, GT Wheels, Infinity Reference 6x8s, Rockford Fosgate P300-10