CliftonGK1

Another vote for the Performance Ultra bibs.

I've got a few thousand miles on a pair, and they're just going to need replaced this season. Many many century rides, 200k, and even a double while wearing the Ultras.

I'm 6'6", 250 pounds and the XL fits well. I'll be buying another pair or two as replacements for my commuter/training gear.
As for high-end bibs, there are some companies who cater to the more generously proportioned cyclist. I'm looking at a pair of Assos FI.Mille bibs for my ultradistance shorts. Their TIR size is what they used to call XXLW (2x wide). Designed specifically for those of us in the 200+ set. And not all of their gear is $350 for a pair of shorts; the Uno and the Logo can be found around the $150 mark, putting them square in with the PI P.R.O.
Now, for comparison in the padding: The Ultra has a very VERY (I can't stress this enough) EXTREMELY thin, low density chamois pad. If your butt isn't comfy on your saddle in a pair of cutoffs, then you will not be comfortable in these shorts. The padding, IMO, is there as a sweat mop and a holster for chamois creme.
The 3D-PRO and new 4D-PRO from Pearl Izumi... there's good and bad about it. It's a high density split pad, so it cushions your sit bones at the saddle and the split offers some pinch protection against having your junk fall asleep. There's a good amount of forward padding, so if you ride in the drops or other aggressive position, you're not riding your unit up over the front of the chamois. HOWever, the cover material is a felted antibacterial porous microfiber. Sure, it feels great even after 3, 5, heck, 11 hours in the saddle... but you'll go through chamois creme like a fiend! Its wicking capacity is astonishing, and when you sweat and start to thin out your chamois creme, that padding will sop it up pretty quick. On a 200k a couple weeks ago, I had to re-apply 2 times during the ride after an initial application just before the start.
As I haven't used the Assos bibs yet, I can't give a personal review; but here's the scoop from the guys at my LBS and some friends who wear them: The chamois on all of them is of the same material, it's the amount and the placement which are different between the Uno, 13, Mille etc. The less expensive ones have a thinner padding than the Mille, which is their ultra-high milage short. (It's also been suggested by my randonneuring friends NOT to wear the Mille for distances under 300k because the price::benefit ratio just isn't there. You don't get the full benefit of the Mille until you spend 20+ hours on the bike, according to them.) The chamois is high-density PU foam and gel, breathably porous, and from what I could tell by checking them out in the LBS, the covering material doesn't seem too absorbent. I think they rely more on the breathability design of the padding to keep them dry, so that they can use a material less likely to sop up your chamois creme. I'm willing to give the Mille a try for my 300k and 400k this fall, and the Uno or Logo a chance for shorter (100k and 200k) rides just to see if they live up to the hype.