Gear choice decisions

AJ/FormS said
If 28s fit, that is an increase of 3.57%, which is a similar loss of cruise rpm.
My math says 50mph=2839rpm, with 4.56s and 27s.
thus 28s are 2737rpm.= 98rpm savings

So 30s would save roughly 300 rpm, about the same as a swap from 4.57 to 4.11.