Healer melding

[Lyrica_Ashtine]

The fact that I can't carry two of the same gear pieces really blows I am trying to find a medium and is difficult wanted to go DET/SS on WHM and CRIT/SS on AST but with not being able to carry same gear and gear being role specific it's a bit of a headache lol

Well, you did mention you like to dps and stance dance regardless of the job. So you should consider how much each point would affect you:
about 44 crit gives you a gain of 1% crit rate.
I have no idea about Determination, but shouldn't be too far off from crit if you compare gear with capped det or capped crit
About 25-26 spellspeed is a reduction of 0.4% casting speed or 62-65 for a reduction of 1%

You have 18 slots if you're in full 220+ gear (that isn't crafted). The ceiling of the secondary stats would be 216 accuracy, Crit rate, Det or Spell Speed. Obviously, you can't meld more on it if the stat is already capped, but let's forget about that for now for simplicity - Accuracy is probably the only stat that can reach the ceiling regardless of gear set, however.
If we'd assume the information provided earlier, the maximum gain would be:
570 accuracy. Estimated accuracy cap for Midas 1 to 4 is 557, 571, 585 and 600 respectively
4.9% crit hit rate increase
Let's just assume it's a 2.45% increase on average healing/damage dealt for determination
3.3% to 3.5% reduced casting time

I'm not going to draw a conclusion here. I'll let you decide yourself

Edit:
According to a reddit post, every 1% crit hit rate after the initial 4,95% base also increases the crit hit damage by 1%.
https://www.reddit.com/r/ffxiv/comme...mage_formulae/