I mean. The fourth one he kinda already was OP. Regeneration suggests a lot of stuff and we now know he did carry over his abilities each time. Aggro Draw is the only truly bad one but paired with Regeneration seems like a good tank combo, mixed with his farsight/precognition ability means he can effectively be a Evasion Regeneration Tank, plus the ability to remove the negative effect of cursed equipment just means he needs to find some good cursed loot.
It is really surprising he didn't become OP in his fourth. And even on his fifth, he technically isn't the one being OP, he has the ability to summon people who are OP for him. So the whole premise might end on him being back at the goddess and getting another reincarnation and that's where the manga ends, just on that punchline.
Also I see that he formed quite a team. His Childhood friend all grown up now who may become a romantic interest, his grand daughter who that's going to be an interesting element of potential complications with his relations here, his best friend hero now king who's probably wanting to repay the favor and will be probably be the ultimate bro/companion, and the mechanical goddess golem doll waifu...
And finally possibly one of the party member that was running away but was hesitating because he was staying back. Seems like she's the intended companion of his fifth reincarnation (and going to appear on his sixth, and seventh, and eight, and ninth, and... So long as he's not satisfied with finally going OP)