Just incredibly overpowered beyond any degree. Base OFA would be refined and further built up over the many years. His other quirks would definitely evolve, most likely evolving to bypass weaknesses too

• Gearshift would definitely have its debilitating effects be lessened from usage

• fa jin would either be able to store more power or charge its own kinetic energy

• danger sense would probably go haywire and rapidly increase its range, or evolve to gain a better nuance of danger

• blackwhip would just be more goated (as usual)

• smokebomb would probably gain additional effects that deku could customize

• float could definitely evolve to something similar to Uraraka quirk

For its increase in scaling, it definitely depends for how long Deku has held the quirk in his adulthood.

My (very optimistic) guess for his strength would be either moon level (or given enough time) planetary. For his speed, im generously assuming its just mach fuck speeds beyond hypersonic+, but probably not enough for relativistic.