Which the above answers my thoughts that in the ideal world the SUT would be built and tailored exactly to the cartridge in question.
Makes it a bit of a pain if you swap carts a lot though......
I can just swap SUTs for almost any LOMC because smart manufacturers like Luxman made at least 3 different toroidal silver plug-in SUTs for one base connected to the arm and phono stage, very easy to swap in 5 seconds. On that page you see 2 of them, but there was actually one more in the middle (8025 for 3-40 Ohm). There is a SUT for any situation, for carts under 3 Ohm, for carts over 3 Ohm til 40 Ohm, for carts over 40 Ohm. But most of my favorite LOMC are all low impedance, anything from 0.17 mV works fine.
Any modern manufacturer can offer something like that ?