I'm actually using Sniper's Edge, my crit is 400+ and the procs is really low, not even 1 crit each battle. Looking at high levels mages equip they handle to stack 5k on crit but the only way to make it is using legend equipment and sacrifice MDEF, the astral and the gems on equip, even so your PDEF and MDEF will be close. If someone have 5k on crit maybe can tell how much it procs more or less.
Till here it's a matter of tastes, but if you toss into the equation the -X% crit damg/rate of enemy equip and the fact that you are throwing about 3k MDEF away (Astral and 1 gem each equip piece) maybe it don't worth.
In my opinion, it's better have a solid +% dmg in EVERY attack and much more MDEF than some spikes dmg, that's what i think after tried both ways, you are at 40 so still time to test yourself before you level up the wrong orange astral
EDIT: Sorry mate gonna get advatage of your post to make a question that comes to my mind right now. (I'm good at maths but the % are my bane, so it's more or less).
I'm wondering, if the range damage is 90%-110% and we equip a lv5 Will Destroyer it will be 115%-125%. Till here all clear, but if now i equip Enhanced Ruthlessness lv4 will my damage be in the 87%-153%? If it's right equip this two astrals will leave you min damage at this base but increase greatly you max damage. Someone tried it?