Admittedly, not being familiar with C300 covers, it looks like both are lower RG and higher diff. I would certainly put a lower-flare layout on them, cover prep would be essential.
The FX is a pearl and the original is a solid. I'd probably go with the solid cover if I'm gearing it towards Nationals.
Also, one of the guys on the Junior Team USA support live stream was throwing an FX. If I remember correctly it was mentioned at some point.