I'm 5' 10' 175 and paddle the Medium Burn. Most days I feel it is the perfect size... but on others I wish I would have chosen the Large Burn. I would say go with the Large Burn if you choose this boat.
I think overall the Burn is a better boat than the Mamba. It has slightly sharper edges which will allow you to play the river a little more efficiently (what limited play you can do in a creekboat).
I know you say you don't like playboating as much now... but I almost guarantee as you progress in your river running skills and you gain some confidence you'll start playboating a bit. Do it all
Hope this helps a bit.
Let me know if you have any other questions.