... that can be mathed out. There is nothing to "feel" here.
For a RDM, 3x100 = 300. That's higher than most GCD spells you have, so at 3 enemies, you want to use Scatter instead of Jolt or Impact. After that, you want to rotate Veraero/Verthunder, as both are 300 as well but give 11 total Mana, which is higher than the 6 you get from a regular scatter. The finicky bit starts when you fully optimize Mana as well.
As for melee combo vs moulinet...
Melee combo as such is 970 Potency for 80 Mana over 4,5 seconds. Add Holy/Flare for 1520 total over 7 seconds.
Potency per Mana: 19.
Potency per Second: 217.1
Moulinet is 600 potency for 30 Mana over 1,5 seconds.
Potency per Mana: 20.
Potency per Second: 400
3 enemies -> E-Moulinet wins in every aspect.
We can now use that calc to see whether Verstone/Verfire procs should be used or not.
We have the potency per Mana calc'd above, but that assumes double Mana usage. Halve it, and you can see how much one point of black/white Mana is worth. It's 10 for moulinet on 3 mobs. Verstone/Verfire are 270 potency and grant 9 Mana each. As such, they seem on par with Scatter - But wait! Scatter can proc enhanced scatter for 16 Mana. You don't even need to calc the exact effect of that to realize Scatter is better, because the worst case already puts it on par.
-> Verstone/Verfire Procs are best left unused in packs of 3.
