I can't recommend the long HDMI (or HDMI-over-CAT5, or long Thunderbolt) enough. The noise isolation you can achieve by doing so is unbeatable. Even moving anything short of a 1U server into a neighboring closet means no perceptible noise, so you're really buying yourself more flexibility such that you can use almost any computer without thinking about noise constraints.
Even more than that, I'll bet a lot of people who are connecting a media PC to their living room TV also have another PC somewhere in the house. With a long HDMI cable, you can connect an existing PC to the TV, thus saving the entire expense of a new PC. This is particularly interesting for gaming, since a good gaming PC is a lot more expensive than even some of the longest HDMI cables.
To add to the HDMI-over-CAT5 instead of long-run HDMI, I wanted to offer an anecdote: we tried doing HDMI with extenders at a previous MSP shop. We had random de-syncs. We were probably far past the 50ft spec for how long to run an HDMI cable and the extenders were unpowered (basically female-to-female boxes). HDMI-over-CAT5, however, handled the distance flawlessly without powered boosters in the middle.
Even more than that, I'll bet a lot of people who are connecting a media PC to their living room TV also have another PC somewhere in the house. With a long HDMI cable, you can connect an existing PC to the TV, thus saving the entire expense of a new PC. This is particularly interesting for gaming, since a good gaming PC is a lot more expensive than even some of the longest HDMI cables.