Rex Rocker
Call me Hugo!
The Classic OD was a Guitar Center exclusive and was about $40 new from GC when it was around. It seems people try to pass it off as some sort of fancy edition and try to sell it for what it was going for new or even more in eBay.both the classic od and gt od go for around $100 new and $50 used so not sure what you mean. they are also definitely not the same pedal, the gt od sounds much better for metal imo.
The white Classic OD came stock with the switch flipped to Zakk Wylde mode. The fatter, middier, louder setting is GT-OD mode. There was also another version of the Classic OD in green. I'm sure you'll find them a lot more similar to the GT-OD if the internal switch is flipped accordingly.
Not sure about the Custom Shop GT-OD, but the later non-CS GT-OD and the Classic OD are the exact same circuit board. All of them have "ZW OD" or something like that printed on the board.