Best hubs for a very heavy rider?

I was servicing a friend's Bulls tonight, when I heard a suspicious noise coming from the front axle. The sound and high-pitch vibration makes me 100% sure that the bearings are shot.
The rear axle doesn't seem to have this and both wheels still spin freely, but it still bothers me. My 6th sense is telling me that the front hub is going to fail in a spectacular fashion if he keeps riding the bike the way it is.

He used to weigh 280lbs and the bike didn't have a problem with that. It was ridden hard (on the road) and has done around 10.000 miles without a single problem.
Then he quit riding due to medical reasons (hiatal hernia) and his weight shot up to the 450lbs region.
Now he's losing weight and wanted to start riding again, so a little while ago I gave his Bulls a complete overhaul. I even inspected and re-greased every single bearing on the entire bike, and they were not showing any signs of wear at that point.
I rode the bike for 30 miles and everything was fine. Now he did another 20 miles and this problem appears, so it's quite obvious that the bearings in the hubs (Shimano HB RM-40, aka. the 2004 Altus set) simply can't cope with his current 400-ish lbs and will probably need more than just a set of new balls.

The rest of the bike seems to have no problems (well, TBH the fork could use some stiffer springs), so with better hubs it should be fixed. I have a spare set of brand new M770 XT hubs, but don't want to slap those on without knowing if they can handle this weight.

Does anyone have any suggestions on which hubs to use?

At that weight I'd go for cup and cone bearings and definitely 36 spoke with halved service intervals until the weight's below 300lbs.

I would not hesitate to use the XT hubs, given the nature of the riding your friend is doing. Once he is able to do more vigorous off road then matters will be different.

Beefy spokes and rims would be advised, of course.

He's only riding it on the road at a normal pace nowadays, so the only real strain on the wheels is the amount of weight they have to carry.
The spokes and rims don't seem to have a problem with the weight, so I think I can stick with the default 32h setup, abeit with better hubs.

I've already sourced some high quality balls and will be taking the hubs apart. If that doesn't solve it, I'll have the wheels rebuilt around the XT hubs.

Thanks for the advice.

Dude, the XT hubs of old were identical to the tandem versions, in terms of the balls, so no need.

They are way over engineered, there would be no problems were he not off roading it.

Later XTs have aluminium axles and smaller bearings. They have already acquired a poor reputation in the touring world. LX / SLX keep the steel axles and larger bearings.

What year?

I had heard something like that.

Mine are the M770 versions, so the 2011 model if I'm not mistaken. Guess I'll keep those for a cheap and nasty build then.

I took the hubs apart tonight, and the cups seem to be ok. The balls show some pitting and in the front wheel 2 of them have flat spots. Luckily there's a bearing specialist nearby, so I'm going over there tomorrow to get the best balls he has.
It may last, it may not, but I'm prepared to give it a go. As much as I like working on bikes, I'd rather spend 20 minutes on a bearing overhaul than several hours on building 2 wheels.

Seriously, they will be absolutely fine for the intended use.

So they were working?

You "serviced" them,

And now they are goosed 50 miles later ?