I have a clean install of Win8.1, I always wipe out the manufacturer's pre-installed OS (in this case Dell) due to all the crapware that comes with it. No 3rd party software like firewalls or anti-virus is installed, it's a plain Win8.1. I also have Ubuntu 14.04 installed as dual-boot, I'll use it tonight and watch out for these issues to see if they happen there, too. I don't recall seeing them in Ubuntu, but I haven't really used it too much on that laptop.
I could live with intermittent delays as I haven't noticed any problems just browsing the web (other than that it takes a little longer if I happen to browse to a site right when the network is down). But when I need a persistent TCP connection to work (like for SSH), this is a deal breaker. I constantly lose my SSH session, which is very frustrating when you're in the middle of something.
Like I said, I'll use Ubuntu tonight and see if I observe the issues there, too. If not, then at least I can rule out a hardware issue.
Also, I doubt that it's interference on 5ghz. There is only one other 5ghz network (far away) that I can see. Lots on the 2.4ghz band, which is why I got this router. But I have the exact same issue when I take my laptop to work and use the 5ghz network at work. Dropping connections all the time, just like at home. So it's most likely not my router, the hotspots at work are a completely different manufacturer.