I'm not sure comparing two different riding conditions makes much sense. Try it when the conditions are nice and dry and have been for a few days and see what speed difference you have. I still think you'll be slower, but not terribly so. Not sure why you'd compare it to a race either. If you're not racing then it's academic really. The only thing that matters is if you're getting the same or better workout during those miles. I'd think with wider tires, you would certainly get a better workout. 5 minutes is nothing when you're not racing.
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