With the Dell MFF having a front USB-C (Gen 2???), wouldn't that give me 10Gb/sec? If so would this be sufficient speed if I bought an external DAS drive such as WD My Book Duo RAID from ebay for £54, which has USB-C connectivity? Would it be enough to use as a combined NAS and a 4 x 5mp Camera CCTV recorder system?Dell boxes are optimized for the exact configuration maximums.
Look at the max transfer rated for SATA and USB3 - for the variety supported by the box - and look at the rated maximum transfer speed of the drive you select. Most 2.5 drives are 5400 rpm unless you specifically get 7200 rpm. i suspect video recording drives are 5400 since the focus is streaming in/out.