I own a 05 600EFI Sabercat & a 2000 Sxr600w/pipes, I ride with two guys with Sxr700 Yams & one with a SRX700 Yam.
Gas mileage goes like this SRX700 is by far the best, & with by far the most performance PERIOD!
The 2 Sxr700s are always $4-6.00 better on fuel than my 600EFI Cat but are outrun by the Cat.
My old Sxr600w/pipes is just slightly better on gas than my Cat but will outrun the Cat & the two Sxr700's anyday, anytime, anyplace
It also has 20,000kms on it with one set of pistons & a new track last year