Since we meet him in Sovngarde during Skyrim, I roleplayed my Dovahkiin sparrign with him - as it could be the only chance for my warrior to cross blades/axe with someone so legendary on friendly terms.
However...
...would even an experianced (i.e. high level) character even stand a chance? As far as i'm aware we don't have a great deal of solid information on how skilled or powerful the ancient king was, aside from 'very'. We know he and 500 pals were capable of a great deal, but we also fight one of those companions on Solsthiem and while skilled he was nothing truly special outside his curse.
So, from a lore perspective how do you suppose Ysgramor weighs in compared to some of the greater warriors of TES lore? Almalexia in her prime, for example, I can't imagine being troubled by a mortal warrior no matter how strong. Thu'um or no. I'm not generally fond of 'power level' threads because they are silly, but this is more just being unsure of Ysgramors ability.