Gai beats the hell out of Hashi then finds out it was a wood clone, repeats until he dies after running out of time...remember Madara was not taking Gai seriously and allowed his power up(and if it's like i suspect and the eight gates originated from Hashi then...pure speculation)
No even like this i doubt Gai could break Gegou mazo...in part one Jiroubou lifted Super Expansion choji with one hand while said choji was trying to body slam him(take not this was an at least 100M choji who's nose was as big as a tree) then butterfly choji who said butterfly mode had that same x100 multiplier caught jiroubous punch as if it was nothing...then as a 17 year old choji goes giant mode increasing his strength then butterfly mode, that's x100 his giant forms strength...this suped up choji connected a full powered punch with the Gedo mazou who shrugged it off as if it was nothing and proceeded to stomp...So think before over hyping gai (his punch hasn't shown to be able to solo a mountain...yet)
as i've said many times before Dbz logic does not work in Naruto/ nor does One pieces it's not a hit it with a larger hammer type of manga...a fodder ninja can beat eight gates gai as long as they know he is going to use it...they could just hid under ground or henge Gai is not a sensor(though it'd be funny to see him get trolled by academy jutsu)