Haven't tested myself yet but appearently the halved perpetuation effect gets added AFTER you subtract the normal avatar perpetuation gear. So for example if you normally stand in -11 Avatar Perpetuation, for a normal avatar you'd be at 15-11= 4mp/tic perpetuation cost, gloves would only do 4/2= 2mp/tic, hence actually giving an effect corresponding to avatar perpetuation cost -2 in the above example. If you also have Augur Legs for a total of -12 avatar perp You'd get to 15-12=3. 3/2= 1mp/tic hence receiving only avatar perp-1 from gloves.
I guess it's still good of course, it's just much smaller than the impression you get by reading that "halves avatar perpetuation cost".
By 99 as /SCH you'll be able to storm 5 out of the 8 elements, you can't Thunder/Aurora/Void. Nevertheless, pair these up with Summoner's Horn from Dynamis and Caller's Pendant for a good perpetuation build.
Or even during the specific day, if you do not have Caller's Doublet +2, you can pair these up with Summoner's Doublet from Dynamis.