I'm not sure how to figure out my 1 rep max for legs for the exercises that require holding dumbbells. It won't be my legs that fail but my arms that can only hold so much. Does that make sense?
I totally understand because I'm in the same boat as you. I did some leg 1rm testing on Friday and I have serious doms....in my forearms and shoulders. I think I'll be using my weighted vest so I don't have to hold so much weight in my hands.
Good luck and let me know if you find anything that helps you.