I quoted the SKF page to show the specs, not that they should be replaced with SKF version of the 6001Z. Of course, if one replaces the bearings one should replace them with better quality AC bearings. To replace 6001Z with similar (but better quality) 6001Z is pointless, or not a good idea.

Anyway, to be honest, I don't think you'd wear out these bearings unless you are a heavy user of the machine. Most hobby users don't run their machines for hours every day, the speed is low (even with fast servos) and is very far from the performance top of those bearings so wearing out will take time. But sure, eventually they may wear out, and in that case they should be replaced, but as I said earlier, replacing is easy and can be done when needed, will result in a few minutes of work per screw, so no big deal.