WRT copper foil / polyester caps, generally polyester are more 'coloured' than polyprop, teflon or polystyrene.
Polyester caps are all the rage with tube guitar amps for that very reason. They have a warmth and 'tone'
that guitar players like.
For hi end it's difficult to say, will just have to try them.
If they are cheap enough I'm keen to try them for gtr amp upgrades.
Z
