Hubby is 5'10" and currently just under 300 lbs. He's built like a former sumo wrestler, and has a belly along with a broad back and tree trunk legs (saying that he's not ALL belly, that his weight is sort of spread out).
The ONLY ride he has not been able to do at all is Maliboomer. The combo of his belly and very broad and thick back keeps the shoulder restraint from being clipped with a tether. On CA Screamin' the shoulder harness is fine on him (he was worried, but happily was able to ride!), but with Maliboomer there's a strap from the bottom of the shoulder restraint that is clipped onto the seat, and he's about an inch, or maybe half an inch at this point, away from that happening. He hopes we can plan another trip before Maliboomer is taken down, b/c he has been losing weight (WW for the last 2 years) slowly but consistently, and thinks he'll be able to fit it soon.
For the Pooh ride, were you in a seat other than the front? I've read that the very front is better for those with knee problems b/c it gives you a bit more room. Or wait, do I have that backwards?

Maybe someone can correct me, but there's a difference between the very front and the middle and back rows. I think it is the front, b/c if hubby, DS and I are riding, hubby sits in the very front and I sit behind (and DS sits with whoever he wants to sit with), but if it's just me and DS we sit in the front. Anyway, it's worth a shot to try again, sitting in a different spot.
Astro Orbiter is obnoxious to get in and especially out of. But if you're riding with a kid it's even harder. Hubby will NOT do it anymore with DS, and since DS is only 4 that means I have to ride it, and I don't like AO. What's a bummer is that hubby really loves AO, he just hates getting in and out, especially riding with DS. (not that he hates riding with our son, but the maneuvering is harder)
He's never had a problem with Space, interestingly. But his height is mainly in his torso, so maybe that's why there are no issues with his legs hitting anything.
Just remember, if you want to ride by yourself it's OK, just tell them. When we are splitting up, instead of saying "3", we say "2 and 1". Seems to work for them (though on another board some CMs said they didn't like that, but we were TOLD to say it like that by a CM, soooo....). No one has ever blinked an eye. So if you are more comfy by yourself, do it. Also, the CMs that hubby has dealt with in his quest to ride Maliboomer have been kind, courteous, and polite. He is self-conscious, and he has been incredibly disappointed, but he has NEVER been made to feel embarrassed or bad or shamed. They try hard to clip the tether, but if they can't they tell him, and he exits. They have been all business. So don't worry about reactions from CMs, and if by some horrible chance you do get a CM with an attitude, take care of that with their manager or City Hall, b/c that is not how they should act.
For the Piglet, BTMRR would be the main one. In '05 I was smaller than I am now and my brother and SIL watched our then 1 year old while hubby and I went on it together, and I was free floating. I don't personally get scared by that sort of thing, but some are. But the main problem was hubby's legs in that case (belly's can be moved, LOL), and that isn't something that's going to change b/c they are all muscle, so we'll never have a time on BTMRR when I'm not free-floating a bit. And DS will ride with me, once he is brave enough to ride it.