@milimetr --
A 1.00mm (no more, no less) solid core wire has something particularly well going for it at HF-frequencies, I’ve found.
Just recently implemented a JBL 2405 Alnico tweeter over my existing main speakers. It’s high-passed at ~11,5kHz 6dB/octave and hooked up with lightly twisted, 1.00mm (i.e.: AWG 19) Mundorf CUW210 OFC solid core copper wires in a teflon insulator. Works excellently.
Mundorf also has a Silver/gold solid core conductor variant (i.e.: 99% silver, 1% gold), in a teflon insulator as well, that comes highly recommended (and is somewhat more expensive). This can be had in 0.5, 1.00 and 1.5mm wire diameters, but again - I’d go with the 1.00mm cable.
Whether to go with the copper or silver/gold variant of the Mundorf cable (or differing conductor materials from other cable brands) depends on synergy and taste. Both options are excellent (I use the silver/gold wires elsewhere in my active speaker setup, and also as interconnects).
Just my findings.