Perrone, Like my son, it sounds like you can "palm" a bowling ball. I am a 1/2" short but 10 years ago could hand hold a D1 with 50-500 Sigma for 8-10 hours. Now at 68 years, the D800 (no grip) + 28-300 is my weight limit for a 6-8 hour shoot.
I really don't understand why you do not use a D4? I would have one if it weren't for weight and price.