They are capable of damn good mileage; some guy who my friends parents used to know had one and always, ALWAYS exclaimed his record mpg of 53 (granted, that may be the ONLY thing you can brag about with a Geo Metro).
My only question, and main concern... is how you'll handle going from the T124, to the C43, to C5.4, to E55 to Metro? I reckon the E55 has more than 8 times the horsepower?
But at 4-500, why the heck not?