The Malibu X-Factor is a sit on top that has a weight capacity of 600 lbs, and is said to have great stability. It is reported to paddle well for a kayak of it's size. The dimensions are 14' by 33".

Surely someone with a 6'5" frame would have fewer problems paddling a kayak that is 33" wide than the smaller guys around.

Also, with the 600 lb capacity, there might be less of a tendency to sink too deep in the water, causing drag and tougher paddling.

An internet search on the X-Factor would probably produce some good information, iincluding reviews. I'm sure there are other options also.

Best!