HDMI switch box to one long run of HDMI cable

I use an Oppo HDMI switch box in a very simillar situation as what you are describing except I ran through the walls and ran speaker cable to speakers instead of interconnect. It works very well. I went with plenum rated cable instead of a conduit. I was unsure if a PVC conduit would have an adverse affect on sound quality like I have read that synthetic carpet might.
I am running about 20' of HDMI cable and have no problems with picture quality.

Cheers,
Jim

Recommend you run speaker cable that distance, not interconnect. Not totally sure about this, but I think you have a good chance of picking up EMI/RFI with interconnects that are that long, the voltages are not that high, you might also get signal loss. 30' of speaker wire would be less susceptible to EMI/RFI because of the high voltage in the line, also cheaper to run, several very good types of speaker wire sold in bulk. Make sure to use a heavy guage.
I run 25' of HDMI, rated in-wall from Monoprice.com, picture looks good. Dunno how much better it would look with uber-expensive HDMI cable, but I'd have to find a pile of money in the street to do the shoot-out. I'm more of a two-channel guy. I don't use conduit either.