I think it's up there, Volk lost IMO, but his performance was a moral victory as he was going up in weight and the smaller guy, despite being stronger.
Pound for pound, you can argue Volk is higher than Islam, though Islam is incredible, his grappling and striking are solid. People think his takedown threat is what makes his striking look good, but the guy obviously has pretty good striking for someone who was born a wrestler. Same for Volk, Volk is a great grappler for someone who basically focused on Muay Thai as the base.