During the restore process in iTunes, I previously had issues with a frozen restore state. My iPhone would restore to just near the end (about 95% along the progress bar) then freeze. I would wait and wait but nothing and it would never complete.
It turns out the culprit is Wi-Fi Sync. Uninstall it on your Mac/PC, and then try your restore again. I totally forgot I had it installed, but removing it will fix this issue.
Download the Mac uninstaller here.
Let me know if you’ve ever run into this issue!