I am planning on getting either the 850 Evo 120GB or 250GB. So I checked the specs and I noticed the difference between two are: the 850 EVO 120GB has 4KB Random Read (QD32) - Max of 94,000 IOPS and a DRAM cache memory of 256MB as opposed to the 850 EVO 250GB version 4KB Random Read (QD32) - Max of 97,000 IOPS and a DRAM cache memory of 512MB (2x more than 120GB version). The questions is: how much faster is the Samsung 850 250GB version? Also, could anyone please elaborate what IOPS, 4KB random read, and DRAM cache memory are? Thanks in advance.