I've spent the whole day learning about rims and tires.
I'm realizing there are a lot of variables.
I found a good website to buy tires. You can basically get exactly what you want for a good deal plus it's easy to see if a particular tire size exists.
Cheap Tires Online | Find the Best Deals on Tires | SimpleTire.com
I think overall the best and most cost effective thing to do for a non-hardcore ecomodder* is to up the diameter on the drivetrain wheels*, keep the non-drivetrain wheels the same (or even go smaller D to help reduce weight and radial inertia) and reduce the width on all tires to the smallest size your existing rim can take (which will probably only be a cm or two so your grip will be hardly effected much but the weight and drag will be lightly effected for the good).
If you are hardcore I would reduce the tire width by an appreciable amount which basically means getting new rims.
You can become hardcore by turning your engine off while on nice coasters and then using your e-brake to slow down so you don't lose break boost. And this should help to wear your tires more evenly if you have a FW.
You can then put the tires on yourself and then get someone with a Cosco card to balance them for like $3 a tire.