The 10" Guide will likely provide a little more lateral support than the 8" Nevada. The taller boot is better at keeping debris and minimizing risk of water spilling in. However, as far as keeping water and debris out, wearing gaiters with a shorter boot is what a lot of people prefer.
i'm a short boot/gaiter guy. the nevada has almost too restrictive of an ankle area for me, but i'm either getting used to it or the memory foam has taken the shape of my ankle a little bit. it felt like it was invading my space the first few times i put them on, haha. the Nevada seems like a heck of a boot for someone looking for some ankle support and a fairly large toe box.
they are pretty good for me now unless i do a lot of uphill in a day, then i start getting some heel slip hot spots. i would be pretty content with them if i could get rid of the little bit of heel slip.... it's not bad, but i feel it after a long day with lots of uphill.
the other day i walked just shy of 13 miles, not a long hard day by any stretch, but i was getting hot heels at the end... the last 4 miles there was 3 miles of uphill, then the last mile was steep downhill... my feet were pretty good until that last uphill stretch, then i was happy i wasn't climbing anymore, i felt like i was riding the line of blisters. next thing to try is liner socks to see if i can remedy that..... my summits have not gave me any foot issues at all. if they were 1/4 size bigger and all leather, they would be the holy grail of boots for me.... they do good in rocky country, side hilling, good traction, enough support for me, but still light enough i can sneak up on stuff and shoot it with my top pin.... the synthetic panels have a shelf life on the coast with all of the thorny brush like salmonberry, devil's club, and blackberries i'm always walking through. they stayed dry for a season and a half still, which is great considering the miles i put on them, but i'm confident they would still be dry without the synthetic panels.
zamberlan guarantees the goretex for the life of their boots, which is very attractive to me. if i find a pair that fits perfect, and get a second pair, i should be able to stay in a dry pair of boots for a couple years, which would be awesome, because it's wet here..... especially Oct-April