loader
As I understand it, once we get outside the "normal" pressures/velocities for a given cartridge, the relationship between pressure and velocity isn't quite linear. That is to say that pressure can go up quite quickly while velocity doesn't seem to change all that much.
If 7.0gr of Power pistol gives you the velocity you hope to achieve, terrific. If I were you I would load up to 1,250fps with the 124gr Hornady and be happy. The extra 50 fps isn't worth the trouble. Absolute reliability and good accuracy are more important (in either competition or real life) than extra power.
As for brass and whether or not you should re-use it, I leave that to you. I was loading Major using a 160gr cast bullet sized down to .356" at 1,100 fps. It was tough on the brass but it did the CZ-75 no harm that I could see. The loads you are talking about would seem to be on the heavy side but no where near what I was running. If you are just shooting targets, reload the brass but inspect it carefully for cracks and dimples inside the case or discolouration outside the case just above the rim that suggests it is being over worked. After awhile you will get a feel for what the useful life of the brass is (3-5 reloads ideally).
If you are talking about loading ammo for serious work, in defence yourself and your family, load once into new brass and use that, or , better yet, use factory ammo.
Incidently, I'd still recommend the Pachmayer grips as the single most useful accessory for a CZ-75. The grip goes from square to nicely rounded and provides a much more secure grip, plus the added safety from a blown case.
Let me know how it works out.