I'm 6'3" also but I'm almost 100 kgs and I find my Hover 125 just fine.. It was a little tippy the first few times but it soon became pretty stable and I think if you went with the bigger 140 L board you would be looking to upgrade to the smaller 125 L board in no time.. If possible you should demo first to be sure.. I'd recommend getting a very large foil (at least the 1650) and it will help you heaps to learn foiling.. I'm using the Hover 125 L board and the big 2450 foil in this vid with the big 6m wing.