What ergonomic chair specs matter most for large-frame or big-and-tall users?

Big-and-tall ergonomic chair specification at OfficeFurniture2go.com: standard range covers users to 300 lbs with 20-inch seat widths. For 300–500 lb users: bariatric-grade chairs with 24-inch seats, 500 lb steel mechanisms, 75mm casters, and 2.5 lb/cu.ft foam. Tall users over 6'3\" require extended-height cylinders and tall-version chairs. We confirm all three dimensions before recommending. Call 1-800-460-0858.