Subjectively to me, the size differences are pretty even spacing, SC64 to SC60x to SC700. Since a SC64 rides in my pocket most days, the SC600x's seem a bit too big for EDC use, and the SC700 seems way too big (esp. the head) for my EDC use. But, my suburban-warrior skinny jeans and khakis differ from people with more a more practical wardrobe, so I bet that the SC700 will end up in lots of pockets due to runtime, efficiency (for a high-CRI LED), heat management, and beam. It has a very even beam, no defined hotspot; so, I use it on my bicycle handlebar (compliments an SC64 on my helmet) for conspicuity and lighting while commuting on paved paths and suburban neighborhood roads.
I think the ZL product comparison spreadsheet has a 2nd 21700 model, so we'll soon have two larger-battery models to choose from. If they ever come up with an SC70 (small-as-possible version of the SC700), I'll reach into my cramped little office-worker pocket to throw my wallet at it pretty fast!