I would actually put Russell on Klay and let Roberson play Steph. Klay is less taxing as his style of play outside of running off picks is less stressful than guarding Steph. To me thats where the Thunder have made their mistake. You play Russell on Steph for 85% of games for 7 games, in addition to how that fool doesn't have a middle gear on offense, and you are asking for him to be burned out.
He would only play Steph on switches,and for them to ask him to be effective offensively, as well as guard up on the most dynamic player on the team, is a recipe for disaster.
I don't know who wins game 7, but for me, this strategy is front and center to why there will be a game 7. Look at who in the last two games, was in the center of the wins... and who was guarding them...