It depends on what you hope to achieve from a speaker cable upgrade. Any people will say it’s just a wallet lightening exercise.
I wouldn’t go that far myself, but upgrades from a very good cable to an excellent cable are unlikely to be massive.
However, you could argue that if the rest of the system would cost mega-bucks to improve upon, spending a grand or whatever on cables could give you a nice little upgrade without breaking the bank, relatively speaking.
Staying within the Chord range would be logical, so going to the signature xl makes sense. To me, the Epic has quite a dense, thick sounding upper-bass/midrange & the SigXL opens that range quite a bit.
Alternatively, maybe TelluriumQ stuff, pick your price point, or I’ve heard some good stuff from Audioquest.