I am 6'1" and ab out 275#. For the past several years I have trusted my life to the "Ol' Man" and Summit climbers , and API lock-ons rated 300#. As big a frame as yu have, look for large !!! The extra width will help a ton. My guess is that "stands" are designed well above this 300# rated weight capacity if for no other reason for liability.

If you have read any of my posts about stands, I have said this before ... and will again ... just be sure to use a high quality body vest. The $100 or so you'll spend is well worth it.