Nemovir, recoil is a function of Newton's laws. If you have energy released, you will have an opposite reaction of the force involved. But note that the formula for energy is Energy = velocity squared time mass. That "velocity squared" is the key point - higher energy comes from squaring the speed, therefore, the more speed, much more energy.
Our black powder roundballs just do not develop enough speed, at reasonable powder loadings, to cause a whole lot of recoil. A .54 round ball is about 224 grains of weight, a .50 is 178, and so on. But at our typical muzzle velocities, you don't get a whole lot of reaction.
I agree with Daryl that there will be little difference in recoil between the English Gentleman's and the Christian Springs rifles. I would lean a bit on the side of the CS - with that "German" flair, the rifle will be just a wee bit heavier, thus less felt recoil. And heck, you could always fill the patch box with lead balls to soak up even a bit more recoil.
Generally, our "old-fashioned" firearms are tons of fun to shoot, and unless you spend the whole day at the firing bench, you won't come home sore at all.
Best of luck to you - you'll find it a fascinating sport and hobby.