Actually all ethernet runs (like CAT5) must be twisted pair wires. CAT5 is UTP or unshielded-twisted-pairs. Coax is shielded so it doesn't have to be twisted.It shouldn't really matter as long as it's not twisted. If either type is shielded that's a bonus. Cat 5 might be easier for future proofing as you can you use it to network as well but whatever you have should be fine for Optik.
If you are not saturating the coax bandwidth, it shouldn't be a problem. I have two comptuers in the basement that are connected to a switch then connect to a STB to share its coax connection. I can push through ~6MB/s of local file transfer to the computer upstairs on coax network without pixelating the live tv on this STB. That is 6MBytes per second. Even if I max out my optik high speed internet, it will never gets anywhere close to 6MB/s. Of course, this is just my results, and everyone's result may vary due to the quality of the coax wiring in your building.You can just temporarily use it, or it will cause problem on the STB.