ok, IF it's a weekend toy that you only plan on putting say, 4000 miles a season on, why not? 4000 miles at 15mpg is 267 gallons, at 20 it's 200 gallons. at $3.50/gallon, that's about $235 extra in gas a season...how many more smiles per gallon will you get with say, an extra 50HP/50tq a 360 will give over a 318 for about the same HP? now if you plan on putting some serious miles on it, then you may want to pay more attention to fuel economy.