Whether steel frame or brass, you wont be wanting to ramp up your loads all that much because of the action type. The toggle link action has long been regarded as weak compared to an 1892 type action, tho they dont cause thermonuclear detonations to shoot warmer loads, as many seem to think. The Henry/66/73 actions are also very cartridge length sensitive, they have to be exactly right to feed. Heavier bullets will have to intude into the powder space. Were it me, I'd stick with standard bullet weights and near factory velocities. For deer, the 44 or 45 Colt should both work fine, with the velocity edge going to the 44 WCF.
"Far better it is to dare mighty things, to win glorious triumphs even though checkered by failure, than to rank with those poor spirits who neither enjoy nor suffer much because they live in the gray twilight that knows neither victory nor defeat." -Theodore Roosevelt-