Only way I would trust getting a female Festae at a subadult size would be from Rapps; I know he typically vents them and gives you the best guess possible. Even then Im not sure the space would be adequate long term. I know females typically max around 9" but it is pushing it a little farther than Id like.
The Siquia/Syn combo worked very well and is still okay, no damaged fins/scales etc. My Syn is a very aggressive (for a Syn anyway) female who had to be moved out of an acquaintance's large display. Once on her own she became very shy so I tossed the Siquia in with her and it has worked very well. The Siquia is just now able to claim 1/3 the tank and wont let anything in "his" space. I want to move him out before any real problems come up.
Oh nice, and thanks for the suggestion. I had looked at Flier Cichlids in the past. They are certainly a cool species which I have never kept.