You do realize that you are dealing with a new vs. six year old chipset, right? While technically the 4 core Sandy Bridge i5 2500 is stronger than the 2-core Kaby Lake G4560, you will have an upgrade path to a new i5 down the road with the G4560 build.
Without question I'd spend the money on a new Kaby Lake build with a weaker CPU then save up for an upgrade. The only advantage the G4560 has is faster single core speed by 200MHz, so only apps that use one core/thread would benefit from the Pentium, and even then, not by much.