I been running this set up for 6months/15,000 miles. Nissan Altima spare rims fit my suzuki siwft/geo metro lug pattern. They are DOT stamped and dont look like donut wheels. I have nice 155/80R15 BF Goodrich tires. rated to 55psi andlike 140mph. The rims are 4" wide so technicaly im one size (1cm) too wide, dont notice and dont care. They do rub the fender well a little in tight turns but its acceptable.
As far as mpg gains. My car is rated 32city 38highway. With good amounts of hypermiling i manage ~44mpg (mostly city) before correcting for tire size. Thats ~50mpg. Did not aba them, and my driving route changed at the same time as the tires so im not sure of the gains from them. but i suspect they get me ~5mpg.
I love how they look too!
And I just covered the rims with $3 walmart pizza pans.
My boss Glenn did a write up of it over on GMF. Pictures Included!
15" Wheels and VW Tires