I've never done that much riding, but I'd say that chamois cream is almost as important as the bibs. I use Chamois Buttr', but there are lots of options out there to reduce chafing and friction. Others can probably offer suggestions for bibs.

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Thanks and I agree. Good chamois cream and hygiene are always the first step!

Assos

Ale bibs with the Double Ergo shammy. Expressly made for this purpose.

Any specific model?

Rapha Brevet.

Assos just released their new product line (S9) which admittedly I haven't tried.
But the last model S7 Milleshorts and Equipe are both great.

The Milleshorts in particular, I have comfortably ridden 7-8 days in a row without laundering them. Probably 5+ years and 15000 kms of riding the same pair of shorts and there's no pilling, rips, detachment of the chamois or anything.

The Equip has a slightly larger and thicker pad as well as different bib straps.

The Assos chamois is huge, goes almost up to my navel in the front, covers the whole dick, gooch and far out to the sides so there's zero chafing in any riding position. The bib straps on the Assos shorts sit just to the outsides of your nipples so there is no chafing either.

I really like the DeSoto 400-milers. I have never ridden more than 6 hours in them, however.

They also have a slit in the front making it easy to urinate if you're a guy. (Your name makes me think you're a guy, but I can't be 100% confident!)

Assos.

Assos here aswell. I never use any cream or anything and i never have any chafing, even with longer rides or riding multiple days in a row.