Sorry OP- I'm looking for advice too...
I feel asymmetrical when I pull sumo with a mix grip. I can double overhand up to 300. Beyond that I have to mix. Conventional pull with mixed doesn't feel as awkward. Just more practice?? Appreciate any input.
Have you tried Hook grip?
Glad to read that my technique is probably good. Sumo is still new to me. I will try mixed grip. I always get nervous of mixed grip though. That's what happens when you spend too much time on youtube and see bicep tears. I'll have to focus on keeping my underhand arm straight.
You should be fine with mixed. Hit 500 today and there isn't an ounce of bicep pain, and this is cinch for from someone who gets bicep pain on other lifts.
Try some chalk or liquid chalk. You'll end up loving it more than straps, I promise.
Hows that liquid chalk stuff working out for you?