Best Tire (For Mpg) For Prius Plus 17" Wheels?

[GoldenKiwi]

I'm looking to replace my gas guzzling 18" wheels and wide tires that came on my 2010 Prius with 17s, and from the research I've done (between the standard package V 17s, Prius Plus, and Scion FRS) it seems my best option is the Prius Plus wheels as at least one person on another forum has said that he did not see any drop in MPG using them compared with the standard 15s. They are also the cheapest buying them from the dealership. Looking at some old threads about the Prius Plus wheels people recommended getting the Ecopia 422s which are no longer available, hence me posting this thread. New recommendations anyone?

Also, if anyone is interested, the prices for the wheels from Toyota are as follows):

Prius Plus - $1,666.44
Package 5 17s - $2,100.97 (Persona wheels are not sold except as replacements for those who bought the package)
Scion FRS - $1,827.32

These prices include CA sales tax, install kit, center caps, and/or lug nuts required.