In a way, it also depends on other things like the turntable and phono amp, device matching, power supply, rack or turntable support. Your Rega RB2000 is a good tonearm and capable of working well with a $4000 cartridge.
When do you know....
If your hi-end cartridge exceeds the resolving power of your arm and you're wasting your money? My current arm is a Rega rb2000 mated with a very old Grado reference cartridge. I'm looking at cartridges at least twice the cost of the arm and I'm wondering if it is worth it. Does anyone else share this dilemma?