Arms warrior - ArP calculation question

Hi all - quick question about how I should be calculating ArP so that I know when I should start stacking Strength gems again...

Here's my armory link: http://www.wowarmory.com/character-s...&cn=Wezmerelda

At the moment, I have an ArP rating of 835 (or rather, that's the number that shows up when I mouseover my Hit Rating), for a 59.66% reduction.

I manually added up all the ArP on my gear (including gems), and it stacks to 835, so:

a) can I reasonably assume that my 10% Arms buff to ArP would bring that total to 69.66% armor reduction? or is it 10% more of the rating, so 83.5 extra pts...??

b) would my 6% 2-pc T9 set bonus bring this to 75.66%?

c) when my Needle Encrusted Scorpion procs (adding 678 ArP), does that give another 48.44% reduction, putting me at a total of 124%? (and that's over cap, I realize).

If none of my presumptions is incorrect so far (please correct me if they are!!!), then I think I can work from the above calculations to figure out when to stop stacking ArP (and when I can get rid of the NES trinket for something more fun) and when to go for Strength.

Thanks everyone for your help!!!

~Wezmerelda