I realize that is a question that requires a bit more information so here goes.
I am a 36 year old guy that weighs about 230#. My commute is 25 miles one way. About 20 miles of this is on a flat MUT. I live in MI, and am not able to commute through the winter as the MUT becomes a snowmobile trail. I live in the country, but commute into Grand Rapids, which is not New York, but still has lots of stoplights and other city cycling problems. I currently make this commute on my Gary Fisher Marin (MTB), which I have commuterized with lights, fenders, road slicks, and rack. Currently, I am a nursing student, and can afford the time to make this commute (90 to 120 minutes each way). I have done a little reading here, and have not seen anyone who is commuting that distance on a FG (I am sure somebody is, but I haven't run across the reference yet.)
I have my first "real" bike, a 1989 Raleigh Technium 450, that I think would be a good candidate for a conversion. There is some sentimental attachment to this bike, but it is currently not rideable, due to a wrecked rear wheel. All other components are workable, but a by today's standards, are far from great. I want to do something with the bike, and converting it seems the least expensive way to go.
So what do you guys think? Is my commute way to far to make on FG? Is my conversion idea plausible?