I think it would be a very reasonable upgrade. You'd have a better high gear and a better low gear. It wouldn't be huge but for road riding it makes more sense. If you can spin at 120 that's quite impressive. There are plenty of pros that spin more slowly than that. Riding more won't get you a bigger top end or a smaller bottom. Sooner or later you'll find yourself on some ridiculous 20% grade thankful for the lower end and in some race going a few mph faster downhill happy to have the better top end. Seems like a no brainer to me if you're road riding.