OK, let me see if I can assist. First off, MotoNation is THE US importer. They can direct you to a local stocking dealer for fitment assistance. Not everyone likes the fit of one particular brand, so it'd be nice if you can try on/compare Alpinestars to Dainese to Sidi to other brands back to back. For your size, I'd probably recommend 44 in Sidi, either 43 or 44 in Alpinestars, and 43 in Dainese (this is primarily for their racing/sport products as I frequently recommend differently for each brand's touring models and US-foot-form models). Here is my take on the Sidi lineup:
Vertebra, Vertigo Corsa, and B2 are all older models and not really part of the comparison. So I'll start at the low end.
Fusion - good boot at a reasonable price. While they still claim to use the Vertebra system, it's really not the same and doesn't offer much by way of structural significance. It's basically a simple sport boot that has decent construction, toe sliders, and pretty much everything you need for general street and even light track use.
Cobra - better protection and materials throughout compared to the Fusion, but not really much added functionality. In other words, it does the same thing that the Fusion does, but does it a bit better with a bit more quality. I would recommend the Cobra over the Fusion. It's $50 more, but IMO, a noticeably better product.
Vertigo - Much better protection, Much better materials, Much better boot. While the Cobra and Fusion have about the same function, the Vertigo adds quite a few features. The adjustable calf area is priceless if you are trying to tuck in leather pants with some amount of shin armor, and/or if you have meatier calves. The inner materials, combined with the openable/closeable scoop vent and the amount of air circulation those two things provide makes it a very comfortable all temperature boot. Honestly, there isn't a whole lot of reason to go to the Air model, even in South Texas (where I am). This boot is an EXCELLENT street boot as well as a perfectly suitable trackday boot for even a pretty avid track rider.
ST - this is the new one that isn't quite out of the shoot yet. I like it better than the Vortice, personally. It seems to be easier to get in and out of. Has all of the track/race level feauters that you would want. It has significantly more ankle/mobility/structural reinforcement than even the Vertigo (closer to what you find on the Vortice). I might look at it seriously if track riding is a significant consideration. If you are 95% street and do a trackday a year, do you NEED the ST? Probably not. The Vertigo is probably completely sufficient. Then again protection on the street versus protection on the track is a question that always leads me back to thinking about street injuries often being worse than track. It's definitely racier than the Vertigo. So you decide if that's called for or not.
Vortice - Outstanding protective piece. If you are a club racer, it's probably a worthwhile investment. On the other hand, they are kind of a pain to get in and out of. So some street riders have a difficult time wrapping their heads around fussing with it every time they want to go for a morning ride. Sidi intends this to be a race boot and it is off-the-shelf pro quality. Lots of adjustment and absolutely storm-trooper level of reinforcement. Do you need it? The OP said street use and possibly future trackday use. So it wouldn't be the first one I'd recommend, but it couldn't hurt to have that level of equipment either.
All of that said, I'd put my best guess as to what you'd like using the most on the Vertigo. But I don't think the Cobra or ST would be bad choices either, and all around Sidi makes excellent stuff, so don't take that as a recommendation against any of them.
Hope that steers you in the right direction. Feel free to PM me if I can answer any other specific questions for you.