I have a pair of Zamberlan VIOZ PLUS GTX (~8") and also the VIOZ GT (~12"). Really like both, but am hoping to make the 12" my primary and the GTX as my backup. Having broken an ankle a few years back, I like the extra stability (actual or perceived) of the taller boot. They are heavier, but I believe I can live with that. Having said that, I am not having any issues with the shorter boots.
Only issue I am having is a blister just above the protruding bone on my rear of the heel ... with the 12" boots only. Doesn't happen with the shorter boots. Lucky I work within 10 minutes of Lathrop & Sons where I bought the boots. After looking at my feet on the first visit, Stephen told me that if I had a problem with boot fit, it was most likely going to be my heel area. He was right. Stephen and James are working to refit the boot to remedy the problem. Interesting to see them get the tools out to remold the heel cup area.
PSA ... I highly recommend talking to Stephen or James at Lathrop & Sons. If you go with the custom fit service it will cost few bucks more, but they will work hard to get you in a very good fitting boot. Both of them are hunters and understand the demands of hunting in the mountains.