How good does my system have to be to realize an improvement with cables?

+1 to what @ghdprentice said about trying before buying. My experience with audio equipment is that it's not so easy to equate price to sound quality improvement. On my $1700 Denafrips Pontus II DAC, I've tried 7 different power cords ranging in price from $15 to $600. The one that sounded best to me was a $94 Supra LoRad power cords. The more expensive Shunyata Venom V10 NR & Synergistic Research UEF Blue power cords were quieter, but also seemed to take the "air" and spatial cues out of music.

The Cable Company has a lending library, give them a call.

A straight 10% is an over simplification, many years ago working in a hifi store, we  wired up systems with varying cost cables, we all agreed that once above $30 a metre for speaker cable improvement was harder to detect than difference. For interconnects once we went into the specialist second tier cables around $150 each the same applied. This was on systems up to $50,000. 

De Beers is now telling us that we should spend 2 months wages on a diamond ring. So doesn't it follow that we should now be spending 20% of our equipment value on cables? 😆

@bjp9738 I had C2600/MC302.  For XLRs I used Mogami and upgraded to Kimber Kable Silver Streak then KCTG.  I purchased them used through Kimber on ebay.

Speaker cables I compared Blue Jean Cables to Audio Quest Rocket 33 and Kimber Kable 12TC.  I preferred the Blue Jean Cables in that comparison because the Kimber Kable 12TCs had harshness in the higher frequencies and the Audio Quest Rocket 33s seemed to muffle lower frequencies.  I did try the Kimber Bifocal XLs and the high frequencies were clear and the sound decay of symbols was natural and the total sound was dynamic and clear.  Much higher price point than the 12TCs but in my system worth it.