In that article postscript we also stated that having such a high level of fitness no doubt contributed to Jason and his team’s success when so many others were failing and flailing. Keep in mind that there is no such thing as being too fit for a major alpine objective.
It’s impossible to set a minimum standard for such a climb. Conditions and weather will make a huge difference. When Colin Haley and attempted a single push climb of the Cassin in 2005 we were quite fit. After acclimating with a W Butt with a sub 7 hour RT time from 14k to the summit and back. We down climbed the W Rib to get to the base of the Cassin. Conditions on the lower Rib we so difficult, black ice and rock fall for 2000ft that we dulled out picks and crampons so badly and had to move so slowly that were were pretty worked before we got on our climb. We had no margin for error so we bailed and climbed back up the Rib.
As you no doubt know, stuff can go wrong very easily on these climbs. I would suggest using Jason’s Benchmarks and trying to hit them. If you fall a little short on some then you’ll still probably have elevated your basic fitness significantly.
I hope this helps.