Also, about using the same 'three' perks.
I have to admit.. I pretty much use Hardline/Scavenger/Tac Mask in this game. Which is odd considering in previous games I never used the perks, or those similar to it.
Hardline I use because I find Flak Jacket and Lightweight pretty much useless.. but I could easily replace Hardline with either of those.
Scavenger because I love spamming those emps! But I suppose I could replace with Hard Wired (for resistant to emps), Toughness, or Fast hands and not really notice, as I die a lot anyway:p
But for Tier 3.. I find Dexterity good for jumping in those windows to get the campers, but I have also found if I hit 'X' enough I can get in just as quick.. But playing without Tactical Mask.. I find it really difficult. Not impossible.. but still..
So for me the perk I really need is Tac Mask.