I find that once a high gravity mead stalls out, there's not much you can do to get it to go much further. I've had meads in the 1.130 OG range finish in the 1.050's more than once, and I've never been able to get them to go down much lower. I'd be surprised if you can get this to go much further, unfortunately.
Did you use a staggered nutrient addition schedule? 71B can attenuate pretty far, but it needs to be babied a bit in my experience.