So you've shelled north of $3,000 for a brand spanking new Mac Pro so you could edit 4K video in real-time and I imagine that, as a bonus, the machine would help declutter your desktop due to its drastically reduced footprint (MacWorld has a nice gallery comparing the system to every day objects).
If for some reason you prefer to use your Mac Pro on its side instead of its default upright position, you can do so because Apple's engineers have designed a fan system to support cooling in both orientations, provided you follow the company's guidelines listed in a newly published support document...