I'm right there with you (6'5" and currently about 415lbs, after regaining a bunch and getting all the way back to 430...). I'm currently on a Trek 820 I picked up back in April (XXL frame) and it's been good so far, approaching the 500 mile mark with it. I went with it for the steel frame aspect - so if it has a catastrophic failure it'll likely just bend vs. shattering like aluminium. It came with nice Bontrager LT3 hard case tires and so far haven't had a single issue with anything (pinch flats were a big worry). Currently riding a mix of paved bike paths and non-paved limestone trails.
Though a couple years ago I did go from about 380ish lbs down to the 300 mark on my old Giant Rincon with some Bontrager H2 hard case tires - but with the previous stress placed on that aluminium frame I didn't want to push it.
I set a goal and once I reach it I'll get a much nicer bike, but if I frag the 820 on the way at least it's not a super large investment...