Mashima could always just swap it up and say Gildarts was just so much more powerful than everyone else (non high Spriggan tier/Acnologia) in Alvarez that his MP is still baffling.
x792 Gildarts vs x792 Laxus. Who wins, what diff?
I'd say x792 Gildarts win with mid-high diff based on portrayal, feats etc. Arguing for anything less than mid diff would be a massive stretch, because Laxus and Gildarts are often mentioned in the same line, indicating some form of portrayal between them.
The Laxus that Erza fought would low diff x792 Laxus. On top of just plain being a lot stronger (stated), he also mastered RL.
If we are going by feats and statements, all the "good guys" powered up even further after the Aldo arc. This Laxus being baffled at x792 Gildarts level power doesn't make any sense.
Forget the powerscaling all together and give me an honest answer. Do you actually think Mashima meant x792 Gildarts when he made that comparison? You recognize how much of a stretch it actually is? We can argue all we want. But Mashima probably didn't think about which version of Gildarts and what not. Like others said here, Mashima clearly doesn't care enough about FT to actually think through this.
The straightforward answer would simply be whatever was the "Gildarts level", that Mashima thought of at the moment. In the context, it likely means current Gildarts level, though logically it's impossible for the good guys to know since they haven't seen him over a month.
Logically though, it should whichever Gildarts they last saw, which would be Gildarts a month or so prior.