I have the exact set up you are considering Cattitude, but with different machines. My main machine is vintage (1957) so my set up is slightly different than yours but I sought out and purchased another of virtually the same machine (1956) for my FMQ. The 1956 model is always set up for FMQ with the foot I like and the proper tension. What I love is that all the controls and parts are the same between the machines so there's no trying to remember how to do anything or having to keep the bobbins etc separated. If you could find a used version of your main machine at a decent price I think that would be ideal.
I can't speak to which machine you should ultimately purchase, but I'll tell you that having a dedicated FMQ machine is wonderful!!