I bought both watches and wore them both for a week at the same time (one on right & the other on the left. If we are talking a 45mm 8 then size is marginal and barely noticeable. As a matter of fact depending on the band the Ultra almost seems lighter and size comparable. If that is your only reason I think the Ultra is worth the purchase and if price is your hangup if you order the 8 in stainless, with all the bells and whistles close to what the Ultra offers, then they are the same price. Also I charged them both fully and used them equally (tended to use the Ultra slightly more) and in 24 hrs the 8 battery was at 7% and needed recharging but the Ultra was at 37%. Then 12 hours later when writing this my Ultra is at 25% and is still going strong. I am assuming it will get at least another 24hrs of battery life then the Series 8.