[Deezler]

Dave, you nailed it; those are the tires you want.

OK, had to check this again. Using the specs provided in Metro's link above:
(btw this is still with the rough gearing estimate of 60mph at 1800rpm). Now using a perhaps more realistic aero target of 0.34 for comparison.

@ 60 mph:

.	mph	rpm	load(kW)	BSFC est.	gal/h	mpg
Cd = 0.42	60	1770.5	11.66	246	0.891	67.3
Cd = 0.34	60	1770.5	9.96	258	0.798	75.2

Cripes! We're missing the target now with stock aero.

But at 50 mph:

.	mph	rpm	load(kW)	BSFC est.	gal/h	mpg
Cd = 0.42	50	1475.4	7.45	265	0.613	81.5
Cd = 0.34	50	1475.4	6.46	273	0.548	91.2

Drive slow and you're golden.

Ok, I saved the spreadsheet this time...