Warmer weather will almost always give better MPG;
1.) The engine warms up faster coming off the EFI choke equivalent.
2.) The air is not as dense to push through.
3.) Tire pressure is slightly raised.
Along with other issues too. This is seen real world all the time. Since I never really take the bike out on cold days my MPG is not affected much. My Sorento looses about 2-3 MPG on really cold days as well.
The DR Pulley sliders will cost some. If you drive HWY speeds it will cost little or even up the MPG slightly. If you do city driving it will hurt as revs are up a bit and since we have better acceleration we all do tend to use it on occasion. Overall the slider make for a much nicer behaving bike.........