I didn’t know RG6Q is quad shielded, but that doesn’t make it any better for a loop antenna, as the inner braid and foil are shielded by the outer foil, leaving just the outer braid to do most of the work. The same goes for any other type of coax. LMR400 is nice and big, but it’s still only 85% coverage, and it’s very expensive unless you can find it in short lengths. Some 10mm copper microbore tube would be better, and 16mm or 20mm Pex-Al-Pex heating pipe would be better still (and a lot cheaper).
But first things first: where is the loop going to be mounted eventually? If it’s going to be outside, a few yards from the house, then make the best loop you can and you won’t regret it. If it has to be indoors then you may as well stick with the RG6, as the RF noise inside the house is always going to affect what you can pick up, especially around the MW band, so see what reception is like first.
I can’t think of any single work which goes into the pros and cons of various loop materials, but you can get lots of useful information just by searching for “small active loop antennas” (probably a lot more than you ever wanted!).