My LM has the +122 will proc on the Rohan ring and the +113 will proc on the hardened barrow brie. From what I could see, on a hit each item independently rolls and if it procs, the proc will overwrite any existing buff. I have seen the +122 will buff with (say) ten seconds remaining be replaced by the +113 buff with a new clock. So although I sometimes lose 9 will from the "lesser" proc, the buff is constantly refreshing, thus providing a high degree of up time. This is particularly useful for LMs because our attacks have long inductions and animation delays/roots, so we are not landing hits as often (plus even in DPS mode we are often pausing to debuff, heal, etc.). I suppose that a class that lands hits more quickly would get enough procs from just one item to achieve an equal amount of up-time, in which case, having just one item with the largest buff would be the way to go.
I don't have two items that proc a crit rating buff, so I'm not able to test for the effects of two items. I'm concerned, though, that a proc from a second item could overwrite an existing buff from the first item (i.e., existing Tier 3 buff replaced with a Tier 1 buff with a new clock). Hopefully that's not the case.
Vikky (105 LM) * Samsgarde (105 Captain) * Iaggo (105 Burg) * Samsgaard (85 Guard, retired) * and various lowbies