Here is the scoop. Resolutions below 1080P are standard speed, 1080P and above require high speed. Howevver there is no magic cut off number. High speed means capable of full badwidth which is more that twice as fast as 1080P. So there may be some longer standard speed cables that will work fine with 1080P, plus there is some fudge factor built into the spec. That is why you see some people using 40+ ft cable just fine NOW.
Now for longer runs your best bet is conduit. That way if you try a cheaper solution and it doesn't work it is easy to change now or in the future as new equipment is going to use full HDMI High Speed bandwidth like 4Kx2K or deep color.
In a nutshell if it ieasy to change try a cheap cable and see if it work for your situation. If it doesn't than use a better solution. If it will be hard to change in the future use a better solution designed for full bandwidht now.