You're looking at a single cell on the graph.
You'd be running two cells, so you'd want to look more at the MD3 18500 run time, and adjust your run time accordingly, based on battery capacity.
Generally, you aren't getting a Malkoff for raw performance, but for reliability and durability (and a great reflector).
Honestly, depending on what you're doing, an M61NL/M61L with a single 21700 might work better. 230 lumens vs 500 lumens isn't as stark as you'd imagine, and the L and LL Malkoff drop-ins are the way to go for runtime. Also, if you run one cell, you can run a single, protected 21700. If your plan is to run these dry, I wouldn't want to use unprotected cells. Malkoff assumes you're using protected cells, so there is no LVP (since these are designed to run CR123A's dead).
Also, I'm not sure exactly which SC700 you have, but that "...can 500 lumens for full 4 hours" might not be exactly the case...?
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