Almost every foe in epic Chronoscope has DR 20/good IIRC (some may be a little more than 20, some maybe less). Some of those foes (the three bosses mainly) are a lot easier when someone is Improved Destructing them.
+7 is still a viable option for an augment, however if you go that way, your eCruelties will be useless in eChrono and you'll be completely reliant upon Cannith crafted weapons.
If you can Cannith craft a +5 Holy Improved Destruction weapon, by all means slot your eCruelties with +7 instead.
I'm not actually slotting them for a while - we'll see how high my Cannith crafting gets, maybe I'll have +5 holy burst silver greater banes for Echrono and epic Devil Assault, and can skip out on good on the eCruelties.