Help me choice Audioquest speaker cables

Better off changing a few capacitors and resistors as cables can vary depending on your components especially if you buy and sell them at various times.

I compared AQ Firebird speaker cable combo with AQ William Tell (Silver) speaker combo ...

Nice to know.  My next speaker cable change/upgrade will be from copper to silver like my interconnects, so I was debating between these same 2 cables models.  Probably go for the AQ Dragon or VooDoo PC upgrades someday also.  The AQ Dragon speaker cables, not within wallet reach but there are other toys...

I decided to hold off on 4ft speaker cables because the AQ WT silver combo including 20% discount new, will run me $6598.92, a bit too much right now.

Please note: During our two month loaner trial on a pair of AQ 10ft Firebird Combo (I only needed a 4ft length).When my rep. returned the cables, they were informed one of the pair plastic termination caps (where the termination divides into 4-connections) was "scuffed" and they wanted my rep. to pay for this. I don't know how it turned out but what a surprise for what was suppose to be a "loaner cable" (keep in mind they sent their second most expensive cable especially at this length) and I assume "New". Bad experience for my AQ Authorized Representative. 
 

So, you were looking at cables over $10K, jacked up a loaner set that you had for 2 months, and now balk at $6k? I feel sorry for your rep and dealer. 
 

Some advice that someone should have given you already: your overall system would benefit a lot more from better speakers and amps than it would cables. Just recently I had your same setup, and it’s “meh”. You’d be MUCH better off investing that money into better components. Given how narrow you have them placed, 800s are far too big if you don’t have more room for them anyway. Go for higher quality smaller speakers and a sub. There’s a set of MBL120s and a MBL amp on Audiogon that would mop the floor with your B&Ws. 

Buying used you get what no one else wants. Read reviews, then search for used. Look for good reviews of cables rarely available for sale used. This indicates they actually work.

People keep the good stuff, sell the junk. Think about it.