Do you plan on putting a fridge into your 4runner in the future? and how do you plan on installing it.
If you want to run 2 side by side drawers with a fridge on top of a drawer, then get a small drawer for the fridge, and a regular drawer.
If you plan on running a fridge, and stack the two drawers next to it, I'd get 2 full size drawers.
If there is no plans for a fridge, get 2 fullsize drawers.
If you plan on running a fridge on top of a fullsize drawers, you will lose alot of outward visibility, and lose alot of usable space.
As others have mentioned, the small drawer's useable space is about 2 inches. Its really tiny. Also the roller floors also cut into the useable space near the edges, due to the bearings (not really a big deal, just annoying). I rather go with nonroller floors and a dedicated fridge slide.
Lastly, while I'm not trying to talk you out of it, but you need to seriously consider the weight, cost, and loss of cargo space. Those drawers are seriously over built and heavy.
I have drawers but I don't have them installed fulltime, because of the weight, and the noise and rattling that come from the gear inside of the drawers, and the amount of space drawers take up.
If I had to do it again, and since I have a fridge, I would not buy drawers again. I'd run my fridge on one side, and plastic plano or packing boxes on the other side of the cargo bay. That way, you gain back some modularity, or freedom to pack your stuff however you want.
Something you should consider before buying drawers on a daily driver. YMMV