They will be a wee bit shorter than stock.
Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
185/60-14 4.4in 11.4in 22.7in 71.4in 887 0.0%
185/65-14 4.7in 11.7in 23.5in 73.7in 859 3.2%
EDIT: Damn it didn't copy.
http://www.miata.net/garage/tirecalc.html