I went through the exact same comparison a year and a half ago (when it was still the SMX-5). I really liked the Sidis, but I ended up getting a good deal on the Alpinestars. I've worn the Alpinestars at several track days, and wear them quite often when I'm riding through town and on backroads. I have no issues walking in them at all, and I absolutely love them. If my SMX-5s ever wear out, I'm going straight to the SMX-6. The Alpinestars are definitely a great choice for street use with occasional track duty.So I'll be getting some new boots soon. I will use them mostly for street riding so I need them to be comfy and at least possible to walk in. I will also be using them for a few track days a year so they need to have good protection and track function. Also to be reasonably priced is a plus.
My main two that I'm looking into are the Alpinestars SMX-6 and the Sidi Cobras. Anyone have experience with these or have any suggestions for others to look at?