[Taxman]

Mine with automatic gets miserable mpg until the transmission gets warm enough (2-3 miles) to lock the torque converter. Then it gets unimpressive mpg for another 5+ miles, after that everything is hot and ready to rack up some bigger than EPA numbers. Switching to 0W20 oil didn't change that, it just isn't ready to go over 40mpg at 60mph until it's warmed up for a few minutes.

Also, I suspect but don't know that the Kinergy tires on most of the RSs have more rolling resistance than the Assurance tires on the non-RS. (My 2017 RS has the Assurance so I can't compare directly)

 

[Taxman]

18 Redline with 18s, Michelin MXM4s I think.
I run 5w30 in mine.

I believe Redline, Premier RS, and maybe Hatch RS come with 18s.
The LT sedans, at least 2016-2017, came with 16s, Goodyears on most, Hankooks on RS, except my fleet ordered 2017 RS has Goodyears.