FIDELITY RESEARCH STEP-UP TRANSFORMERS

Dear All
Like many before me I am moving down the multi tonearm route. Amongst the arms and cartridges I have are a Fidelity Research FR 64S and denon DL103. I was thinking about trying out one of the Fidelity research step-up transformers - preferably an FRT 4, or FRT 5 - I hope to get an FR7 cartridge at some point.

I was wondering if someone could:
1. shed light on the hierarchy of the transformers ie was the 4 or 5 the better model
2. would they work well plugged into any MM phono stage
3. what is the general hierarchy of the step-ups
4. Do they work well with modern cartridges - ie my shelter 501, transfiguration temper v, Benz LPS

I am hoping that someone will be able to help me

thanks