I had audible gains putting a Cisco 2960 switch before my Etherregen and using fibre between the 2.
Which SFP modules you use apparently will affect the outcome though, I've only tried a pair of very cheap 2nd hand cisco ones that are not particularly fast nor particularly long ranged. I can look up what they are if necessary.
I've got a rfi/emi filter on the powerstrip for the cisco and a power cord with a pretty chunky ferrite for it. I have it on black ravioli base and footers too.