You can fit 1k in the 3800 with 5 x 20 racks... but not much spare room!
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And remember folks if double stacking open racks in a 4800 you need a "floor" beneath to correct the height issue. Chips need to sit above the lip of the case so they press into the top foam and hold your chips in the racks for transport.
Floor can be whatever you want but between 3/4" up to 1" thickness. I took some pictures today for another member. Should probably make a thread for it since I get asked all the time.