Is High End Cable Really Worth It and What Brand

As has been stated many, many times on this forum, it's more about system synergy than anything else  - certainly more than price. 

I've been in this hobby for over 40 years and have tried lots of different cables. While I certainly believe that cables make a difference to the sound, I've generally found I get the most bang for the buck using a cable made in fairly high volume using machines (not hand-made) with high quality materials.

While hand-made cables can be good, there is a lot of inconsistency in production, and the labor adds a lot to the cost. When I say hand-made vs machine, I'm referring to the actual cable itself, not the termination. 

In the last 20 years, I've made many of my own cables by using high-quality bulk cable and terminating myself. This allows me to get the exact length I need and use higher quality connectors than are often used by cable vendors selling complete cables. And save a fair amount in the process. 

There are a number of companies that sell good to excellent cable in bulk form including Neotech, DH Labs, Cardas, Canare, Kimber, Mogami, and others.

It's relatively inexpensive to experiment and find the best cable synergy for your system. In many cases, the connectors can be reused for another cable if you're not happy. 

If having great sound is important to you get PURIST asap!!!

 I've been waiting eighteen years for that answer!!

A reasonable priced cable that sounds very good in my system is Canare 4S11 "Star Quad".  I ordered mine from Blue Jeans Cable, if you do so make sure the terminations you ask for are compatible with your amp and speakers.  A Mc I used needed small forks, not spades.

As you are working with a dealer, he should be very glad to let you try the wire he claims is better for your system and you can judge for yourself.  That is the only way to tell.  And I do agree that wire is very system-dependent.  With one set of speakers I own, Blue Jeans 10 gauge sounded as good as some expensive cables I own.  With another speaker, the BJ made the piano sound shrill and harsh, but the other cable was worlds better. But after your system is together, I would try it with the wire you own and then borrow the wire your dealer recommends.