Really?!?! I've got just the Via mobo you're talking about, sitting right here beside my desk!!! I ordered it for my freenas and wound up using a 600mhz Via instead because it worked just fine for a freenas... Will the 1.0ghz Via play h.264 encoded mp4's ok?? No way it can play hi-def can it??
I'm not sure what your point is exactly... but I think the difference between running freenas and a complete Core is pretty large. The Core has many more processes running and many of those processes are quite heavy and media related in a typical system. Yes many small, cheap standalone NAS's use something of a similar or lower power to your 600Mhz C3... but on the other hand they are not intended for useage at the kind of intensity that 2-3 MD system will impose on a Core... a bit of light file serving and streaming maybe... but running all the things a lmce Core has to no.
A C7 @ 1Ghz with a CN700 or CX700M will play an h.264 stream ok in our experience and we run ours at 720p... but a 1.2 or 1.5Ghz processor will improve overall responsiveness in the UI but has marginal performance gain for video playback in our experience.