It's their new marketing to confuse people....lol.
Basically, the gold bottle is equivalent to the "Castrol Edge" of y'olde..
And the black bottle is equivalent to the "Castrol Syntec"" of ye olde.....hehe.
They've simpled made a play on words, and it's "all" under the "Edge" name now, but they are now touting "Titanium" as an additive in their "previously labeled" Castrol Edge And well, the old Castrol Syntec, well, not much new there, they got "Syntec technology" I guess :P
You can't find the Castrol Edge, Gold bottle, in 5+ or gallon containers anymore. They only sell it in quart bottles.
You can find the Castrol Edge with Syntec in 5 quart Jugs and in quarts.
I picked up quite a few of the Castrol Edge, Gold Jugs, on clearance at Walmart not too long ago. They were all SM, GF-5 and did not have Titanium.
I picked up 4, 1 Gallon Jugs of the Castrol Edge, Gold Jug, on clearance at Kmart recently for $14 each. They also had the black jugs of Syntec and Edge with Syntec in Gallon Jugs on clearance for $15 each.
IMO...it's all Edge and they needed to find a way to get rid of the Syntec, because of the synthetic controversy with Mobil, so they mixed it with Edge and renamed it Edge with Syntec....in the black Jugs and quarts.