IIRC GBL auto-induces its own metabolism doesn't it? I forget though if this was more rapid clearance of the drug or induction of esterases responsible for opening up the ring.
There is one thing I think worthy of consideration though with GHB in abusive doses is the massive salt loading one is subjecting oneself to. I shudder to think what it would have done to my kidneys, BP, etc. had I been burning through a couple of hundred grams worth of Na+ in a day when I had a GBL habit years ago.
I have to disagree in terms of the case of 24/7 dosing. That is going to be a hospital job, if your using large amounts. Given the extremely short half life of either GHB or GBL, that is IMO a large part of what made it dangerous. I'd start to withdraw within a couple of hours, and I knew when I couldn't avoid it any longer and had to detox, it was going to be a hospital job, had to plug small doses within a very short time to stay functional and seizure-free long enough to write a guide for the hospital on the pharmacology of GHB/GBL and the likely way to manage it if/when the shit hit the fan, such as that extremely high doses of benzos if used alone may be needed, baclofen being of potentially very large value in treating acute withdrawal (and some other more personal stuff, such as my being autie, not necessarily responding like a neurotypical might do etc.
Had I been using GHB-Na, christ, I would have probably have gone through more than 1kg a month (fucked if I'm working out the stoich, I'm sleep deprived, my knee and hip hurt like blazes, and I'm starving hungry, so I really cannot be bothered, even if I wasn't dyscalculic

)
Which would have been a massive amount of Na+ to have introduced dietarily, hypernatremia terrority possibly.
I wouldn't say GBL is hard on the body to metabolise to GHB, the esterases present in plasma will do it pretty quickly.
Never taken 1,4-butanediol, but being converted to an intermediate aldehyde before metabolism to GHB, that would make it much harder on the body IMO, aldehydes are often rather nasty, if ingested.