[PsYcHe]

Across an axle is more important.. but not essential but I'd be more keen on at least the same standard.

you can do either 1 or 3% out in circumference, but that's more than a worn tyre, so you're fine there. Fronts still wear a bit more than rears. 20s are anything up to 200+ a corner, depends on whether you go for part worns (60+) to brand new.. falkens, chinese specials, or all the way to pirelli or michelin.