My first experience with GC was with the newer light golden colored formula. It was much lighter color than any oil I'd used previously. It did darken up quite a bit in a short period of time, though. Right now there's ~4000 miles on it, and it's so dark brown I can't read the lettering on the dipstick.
Vehicle is a '01 Dodge Durango 4.7L with 128,xxx miles. It's recieved faithful oil changes by the previous owner every 3K at the Dodge dealer using whatever bulk oil they use and Mopar filters.
When I got it, I started using M1 since I had a lot in stock, but switched to Schaeffer Supreme 7000 once that was used up. I had oil consumption with Schaeffer's that wasn't there with M1. It drank a quart in 3500 miles, which really surprised me.
Now that I'm running GC, the consumption has decreased, but it still consumed roughly 1/2 a quart in 4000 miles. I run it pretty hard, so a little oil consumption is to be expected I suppose.
I planned to do a 5000 mile OCI this time, and if I decide to keep with it, I'll go 7500 miles thereafter. I'm sure I could probably go longer, but even at 5000 miles, the oil gets black as tar, so I like to get it out of there and replace it with fresh, if only to please my senses by seeing "clean" oil on the stick.