Here on Old Gobbler, the benchmark number we use for a 10" pattern is a minimum of 100 pellet hits. If your Remington 2oz, #5's were only doing 50 pellets at 40 yards, it's clear that choke/ load combo has not met the benchmark.
Lead #6's have 225 pellets per ounce compared to 170 pellet per ounce of lead #5's. This will give you approx 450 pellets in a 2 ounce load instead of 340. Lead #6's pack more than enough energy to drop a gobbler at 40 yards.
Don't be afraid to try other chokes and loads with your gun if you're not satisfied. The pattern testing is half the gun of turning your shotgun into a hard core turkey slayer.