Within 100 yards a lead bullet starting out at 1400fps would only shoot a little flatter. However, it's irrelevant because a 7-1/2 to 8 pound Paradox gun is not made to shoot a 750gr bullet that fast. When I need a rifle I use a rifle.

Thats not necessarily so.
Leslie Taylor saw the shortcomings of the Holland paradox and cartridge but also its potential. When the Holland patents fell away he introduced his rifled choke version of the Holland gun but designed a higher velocity cartridge topped with a pointed capped flatter shooting bullet to go with it. Now you truely have a shotgun and 100yd plus rifle all in one "the Explora" shooting a 730gr LT bullet at 1250fps. He then introduced the Super magnum Explora gun shooting the LT bullet or a rounded paradox waisted slug at 1500fps for close in dangerous game.
This was not lost on Holland and they in turn offered magnum guns and experimented with various capped bullets. While WR Exploras and Super magnum Exploras loads were standardized, I believe the post 1900 Holland 12's varied to some extent. I have seen guns regulated to various cordite loads that must have also varied the regulated velocity. The weight of these guns were still at 7.5 to 8 lbs or maybe a tad more.