Would it make sense to "load" test by having about 8 people sit/ride in the stern of your boat while at dock/anchor and also taking a ride to see the effect of the extra weight including getting up on plane. Keep in mind that the extra weight is probably not as far aft as the 850 # is probably positioned by the dinghy, so additional weight might be more representative.
I would guess that it might not matter on plane if you use trim tabs although you probably will burn more fuel. I notice that my 43 footer, 14' beam gets up on plane better (at lower RPM) without a full load of fuel and water, a 52 footer may be insensitive to extra weight.