Have Smartboard working all fine with 11.3 on Windows 8 on older 'black' 500 series smartboard. Just needed to manually install driver for the old serial to usb cable on these which are not supported anymore by smart. Got them from pnpdriver folder from older laptop still running version 10. (Pnpdrivers64 for 64 bit) That's within program files/smarttechnologies folders. Just direct device manager there. Took me a few days of trying different versions and thinking was going to need new boards but all working tip top green light now. Hope this helps someone.
Also applies to W8, this has worked for our x64 W8 clients.