Milspec gives you BOD * 3 Encumbrance rather than BOD * 2, which makes it the best soak armor for BOD 4 through 7 characters (barring Soft Weave, which didn't exist when Milspec was design from a mechanics perspective). Most military or high end corpsec that are not Orks or Trolls will be in that range. Only Orks and Trolls can hit BOD 8 unaugmented, and even those specimens are not common (BOD 8 Ork is well above metatype average, BOD 8 Troll is a little above average)
A BOD 4 Human can wear Light Milspec for 12/10, which is better than the 11/9 he'd get from FFBA + Stuff.
BOD 5, Red Samurai + Helmet at 15/15 or Medium Milspec at 14/12, again better than 13/11.
BOD 6 or 7, Heavy Milspec + Helmet at 18/16, which bests 15/13 or 17/15 from stacking.