Additional info:
I have 300 miles on my marathons without a flat on either the slicks or regular. I didn't want to put a slick on the rear and figured if I had a flat, I would rather have it on the front as it's easier to fix.
Secondly, weight should not be much concern. Rolling resistance may well be a factor. Remember the extra weight only counts a bit on acceleration. Once up to speed, it doesn't matter if weight is in the tire or the rider. A pound is a pound. Unfortunately there is no national standard for bike tires with codes for: wearability, rolling resistance, flat protection, and maximum load. In at least one details IHPV article comparing tires, rolling resistance variances were not a signficant factor. The study was slanted towards bent size tires, but if extrapolate to road tires and commuting I don't think it is significant. I decided to accept the higher weight of the marathons and a small weight disadvantage for the major advantage of not stopping regularly to fix a flat.
I've reduced weight of the engine and improved it's horsepower, so I am faster now on the marathons than I was on the lighter weight michelins. Your mileage may vary naturally.