Tom is right, the 103 is hard to beat when going to a mid-priced high-output MC. Like you said "I actually have a valuable Coph Nia with 60dB and can't imagine to go down to 40 dB."
Going to 40db, this is difficult, you will need a step-up like a, M.A. COTTER MC Step-up Transformer.
The cartridge of choice,in your price range is the
Shelter 501 MKII. This is the one Twl, myself and many others here on Agon use.
You might just try getting the Shelter and matching it with your Coph Nia. This is definitely a move up in fidelity. Good luck!