Will one cable upgrade make a noticeable difference?

That's one of those questions that's impossible to predict, as the results will differ with every system.  If it makes any difference, I'd guess that it would be pretty subtle, so may take some time to notice.  The only way find out is to install them, and give them some time.  

Best answer: Only one way to find out. All others are nothing but guesses and predictions. Order the darn cables and see for yourself!!

In general,…

Yes.,, a cable upgrade is a first step wherein one would hope for some audio improvement uptick that depends on the cumulative and compounding fsctors immediately below
BUT… if you are hoping that your particular single cable upgrade alone in isolation is that reward,,, , think again, Alone, it’s highly likely to fail for any Jesus moment or “ A-ha’ moment by itself..Read on.

In more detail:

Hoping for an audio performance major uptick is not a strategy for success. Think full system effects instead:

(1) ergo, think full system audio cables synergy and its system audio performance upticks. Sure, an individual single cable upgrade a good first step in that series upgrade plan. However, It’s a sum of the parts cables alchemy comprised of ALL of interconnects, speakers, power, and ethernet cables.

(2) +1 for @knotscott @thecarpathian …your bespoke system in its cradle-to-grave totality will predicate a bespoke audio improvement.that cannot provide a predictable assurance in these response posts,

without prejudice to the foregoing, it’s your bespoke system that will dictate whether the power cord, versus IC versus speaker vs Ethernet , that may give you the greater degree of improvement.

My experiences = my take: start with a quality build power cable first IMO.Just sayin’….

This is journey of hands-on experimentations by rolling up,your sleeves, , and never a one-size- fits-all quick fix destination.

Yes the only way to know is to try. 
I’m also wondering why you are using RCA there, doesn’t Pathos have XLR in? When you try new interconnects see if you can try XLR version.