Gold vs. Black SRF

I've had both and I don't believe the Gold is worth the extra money. 

I have only had gold one time (black is my standard SRF buy) and for a once a year treat I could tell the difference (or told myself I could) in terms of texture.  That said, I would go with black unless you are serving an extremely discerning crowd.  I doubt any could tell the difference.  Sometimes you can get a prime grade to get right up there as well.  But in general, the higher the quality of the cut the better the end result.  FWIW-

Agree with the above.  Gold is definitely great, but even compared to a Prime I wouldn't say it was twice as good (or worth 6 times the price).

Go for Black. 

I will say that on a consistent basis there is a texture and taste difference between Costco prime and SRF black.   I cook black grade around 5-6 times a year (and at that pace get no SWMBO blow-back); always with some sort of celebration aligned; National Brisket Day, Father's Day, B'day, Saturday after Thanksgiving and some other concocted events.  That said, you will get excellent results with Costco prime briskets which I cook whenever the brisket mood strikes.
You can certainly debate the cost per pound between the two cuts and likely land with the Costco cut and all will be well.  
BTW- I have convinced my M-I-L (who is in her mid 80's and lives in San Rafael, CA (brisket country for sure)) that brisket tastes better than prime rib (the ribs are always CAB graded).  FWIW-

Any solid cook can make a mediocre cut I'd meat " sing" and a bad cook can ruin a quality cut...same in any trade...then take a solid cook and put a quality cut in their hands and OMG....my 2 cents ...