I had a top line versahauler for my tundra. I used it to occasionally cary my 450 dirt bike which is around 250lbs.
Personally, I wouldn't cary more than that with it regardless of the spec. To me, there is more to it than the weight a pile of steel can cary. Securing the bike is a bit wonky and loading a 500lb bike would not be for the faint of heart.
If you have no other choice, go for it. If you do, I suggest the bed or a trailer.
Just MHO based on experience.
Lots but currently:
2012 BMW GSA
2012 KTM 350 XCF-W