Did someone say my name?
Anyhow, to Marco!
My FOX shocks are sublime, I've had them for a few years now and I've played with spring rates a bit and dialed the shock settings in too. For street use I can't imagine there's anything "better". They don't squeak or rattle and they have an excellent amount of travel; suspension travel is much more important on the street/back roads rather than a smooth and well-maintained track.
For the record, I've never driven on Xidas coilovers, so I honestly can't comment on their performance or what they're like on the street. The FOX's are serviceable with OEM parts (bump stops, hats, washers, joints, etc) which for me was the selling point. In 5 years time I can take them off and replace them with readily available parts without worrying about whether Flyin' Miata is even still in business.
I'm sure they will be! But it's the peace of mind knowing I can get parts from any Mazda dealer is irreplaceable.
It also says a lot about FM's thought process when designing the setup. The coilovers are miata specific and built from the ground up using OEM parts. I find it humble that a major aftermarket company hasn't said "we can do better than they did"..
HTH!