If you aren't getting sparkles or worse, you cables are fine.
High speed cables are recommended because they will handle any HDMI signal and there is little price differece. There is no guarantee that a standard cable will work with anything over 1080i/720p. That doesn't mean it won't work at higher resolutions for a given application. But you will have to try it to find out whether it works or not.
I believe that cable length is a big variable. If you have, for example, cheapo 6' cables, they may work just fine. The cables sold as high speed just means that they've been tested to the HDMI spec for this level and passed.