Purchased a brand new Ibis Ripley NX and chose the standard S35 aluminum wheels (1880 grams). Have an opportunity to jump to the S28 carbon with I9 hubs (1580 grams) for a decent discount ($1400 rather than $1800). I don't plan on running anything larger than 2.35 tires. Is the weight difference and hub upgrade worth it? I'm not sure if the I9 hubs are substantially better not than Ibis hubs (in terms of friction?). Any thoughts would be appreciated...or any ideas on similar wheel upgrades for that price point or lower that would be better???