Luffy is at its peak (max lvl)
All 3 haki( all advanced)
DF awakening
.......
.........
As per one piece power system there's none beyond this.
The only problem is time limit.........and always has been for Luffy.
And it was barely 1.5 chapter and he was at time limit again( unless he restart his heartbeat like he did against Kaido)
If there's a way to make Luffy go in G5 without needing to worry about any time limit that would be the last powerup he needed and would complete his peak strength
G5 seems unbeatable while it is active,
Kizaru never did something impactful to G5 other than slight cuts.
He only buys time until G5 runs out of time
One clean hits from G5 did more job than whatever Kizaru done to G5. You just know what I'm talking about.........
Nobody beats G5 unless he runs of time.
Only BB as an EOS material is giving run for his money.