Two days ago I made my first flight with the 727 CS in FSX, I never done before for performance meaning. I really enjoy it, I used the civia all along the route from KMEM to KMIA and at the end I was vectored form ATC to land safely on rwy 26L.
I had to say that KMIA is hard in framerate even on default scenery, I got around 10-12 in framerate at the arrival wich was annoyng.
I used also as backup vasFMC just in case that atc ask for particular procedure where  FIX can be hard to find with vor navigation.
I used Vasfmc also in a couple of flight offline without any problem I just active HDG SEL on the 727 autopilot and active AP couple in VAsFMC and it follow nicely the route.
If you have a good and powerfull PC with a lot's of ram I think should be fine and other area in FSX are more FPS friendly then florida.
Have fun on the 727 office and see you up in the vatsim sky ;)