I have some Audioquest solid wire I bought around '93, like OP's, but mine was flat. It was nice. I also had stranded wire, high purity etc. It was nice too. I combined them, and it too was nice. I also bi-wired, solid for the bass, stranded for treble. I heard no difference between any of the variation.
The first time I heard a truly 'better' wire it was XLO; I still use it. I have some Cardas and Linn speaker wire in a drawer and should try them again in a proper test. But I don't enjoy playing around with my system like I used to — only if I think something might be a big improvement: a real component (eg cartridge, tonearm, preamp, power amp, speakers etc). I don't consider wire to be a 'component' in that sense, the effects are minor. Important, yes, and every little bit counts. And redoing an entire system with better wire can make a very satisfying difference. Just my two cents (which are not even copper anymore, much less high purity).