When people ask questions they could easily answer by spending a minute reading, you should avoid rewarding their laziness. Doing so encourages them to just do it again the next time they have a question. Additionally, if that's the best you can spell please do us a favor by not posting again. You'll just end up with more points.
tokkah, as you can easly find in wowwiki 12.31 ArP rating=1%, that means grim toll proc is worth 49.7%.
however for your other question, this is correct - i assume that theroticly you could reach enough ArP from gear to make gemming for ArP better, but then it would also be bettert to switch trinket..