Originally Posted by Fellwraith

Yes, Arp gains effectiveness the more of it you have, all the way up to the cap (whether you have a proc trinket or not). That doesn't mean it's a net dps gain to change all of your gems from str to arp. Depending on your other stats, it will vary as to when arp is better incrementally than str point for point.

Your question is answered by the spreadsheet if you do what I said. If you're gemming for 240 str, you put a -240 in the strength adjustments and a +240 in the arp adjustment columns. It's very easy to determine which is more dps just by looking at the total dps before and after the adjustment.