After reading all the published papers by real engineers on the subject, and doing the impedance calculations myself, I am still convinced that plain old resistance is the dominant factor by about 100:1  So, 10 gauge twisted pair seems to still be the rational choice. 

You can pay a lot more if you wish, but for actual sonic improvement, I doubt it. 

Amazon:  KnuKonceptz Kord Kable 10 Gauge  $51 for 50'

I did not like the bright blue so I slipped a length of expanded sheath over it. 

+1 Auditorium 23. I’m using them with several low watt tube amps including a Decware ZMA. I learned about them from watching John DeVore’s YouTube channel.

@tvrgeek, I use the 12/14&16 gauge for my basement setup, with nice results. 

My main setup, I use, Furutech OCC wire. FS-36, made a significant improvement over the Monoprice 4/12 I was using before.

I have a couple pair of the Western Electric speaker cable as well as ICs. Member here in AG who makes them does awesome work, really great member to work with, excellent communication. I’ve had them with Klipsch H 4’s, Tyler T1’s, and Volti Razz. I really like them, not thin at all, in fact quite the opposite. I find them very full and sweet. I also have Nordost and IMO, simply disappear, I haven’t found them to be thin sounding.

IC between pre-amp and mac240, and a source to Pre, excellent 

DH Labs Q10 (silver clad over copper) is what has worked best for me, with both Harbeths and Maggies.