The converted MTB will make a fine commuter with studded tires. I used this approach early on and have never gone away from it. I just simply switch to narrow slicks for the summer and the ride seems refreshing all over again year after year. It only hurts a little when switching into the knobby studded tires on Thanksgiving weekend because it makes the bike alot slower until you get used to it. The winter commutes are always much slower due to several factors so you will have to allow more time as compared to summer time.