Quote (djester @ Jan 10 2018 09:35pm)
You should definitely upgrade new ones, don't unequip the ones you use. Personally I think you can start using Caldesann effectively starting with Level 50 gems. The game will let you do this even earlier than 50, so if you really need a boost, then why not? You can always re-upgrade with a higher gem later.
It's all a matter of how much you are willing to grind for grift keys, and then a matter of how many times you are willing to grind out the gems on lower level grifts.
This is why people make alternate characters specifically geared towards speed running. Basically, you just need a build that's strong enough to speed through T13 / ~GR60 and then you focus on mobility instead of damage (or survivability). You can then use this character to feed grift keys and/or mid level gems for Caldesann to your main.
This