I think it depends if you want the look of it (big gun with a belt of dummy rounds around your neck... ) or just something to perform the LMG/LSW role.
Cuz in the end, that's what you're paying for... looks. Performance-wise they arent really doing anything your FAMAS isn't (as far as airsoft is concerned). So in that case I'd go with attack-beacer's suggestion and make a LSW instead: MG36, AUG-HBAR, or RPK/RPK-74 (Aper had a really nice RPK he made). STAR is also supposed to put out an L86A2 when their L85 series comes out.
Or if you're bored over the winter months, you can try building yourself an M2HB