Neither Spence or Clarke will be killing penalties, and neither will be able to thrive against heavy physicality. The right thing to do is to go with the kids and plan a big run a year or two down the road when all the young talent is acclimated and hopefully thriving.
But that isn't happening here. The real issue is Doughty. He won't be able to play big minutes forever, so you want the kids to take over those key offensive spots. However, if you go with Spence and Clarke next year, your matchups are screwed if you are looking for immediate results. Roy does so many things well that losing him in those situations and replacing him with smaller, inexperienced offensive-leaning kids will be a severe blow. Also, Doughty will not accept being taken off of the PP, so what's the point of carrying two similar players and not using one to their premier strength while being significantly weaker in other areas?
Its not an easy decision to make.