CZ 75 SP-01 or Custom Shop?

I'm new to the handgun scene and have been looking for a 9mm for home defense and target shooting. I picked up a CZ 75 SP-01 at a gun shop and loved the feel of it and after doing some research found that they're very highly rated. Can someone tell me what the difference is with a standard and custom shop version and if it's worth the extra money? I have a friend who does competitive shooting and would like to get a gun that would allow me the possibility one day or at least some serious target shooting. Thanks for the advice!

Without getting too technical, most competitive firearms have had sight work, trigger work, grip work, barrel work, etc. Sometimes, that work costs more than the cost of the original firearm, depending on the firearm.