Heathen Sol,
WRT calibres / types etc, in a word - No.
If you need to know then you already do....
Kevlar is just one type of armour, you could also use ceramic or good old steel plate. Each has advantages and disadvantages for rotary applications.
I'm not getting specifically at the Merlin; the "2 out of 3" comment applies to all rotorcraft in Afg - Even the mighty CH47 won't be carrying 55 troops in LFO, full tanks and BP over there. It's just that if your disposable payload is relatively small, things like BP rapidly eat into it.