Basic, 'on paper' efficiency values that I threw together.
MM atma (10/tick refresh)
That /rdm maintains Refresh 100% of the time, for an average +2.2 MP/tick
That one refresh tick (either 10 or 12.2 MP) occurs per cast (ie: avg of 3 seconds per spell cast, even though the spell itself won't take that long)
Close to max cure potency, either through gear or including Rescuer atma
That all cures are hitting for near max potential (Cure4 & Curaga3 for 600, Cure5 and Curaga4 for 1100, Cure6 for 1500)
That MP pool is 2000 MP (may require Allure atma for non-Taru races)
That /sch gets two Penury uses and a 275 MP Sublimation when burning through their pool
That /rdm uses 100% of its pool before Convert. In practice it will lose about 5%-10% of that.
Cga3/3 is Curaga 3 hitting 3 people; Cga3/4 is Curaga 3 hitting 4 people. Same for Cga4/3 and Cga4/4 for Curaga 4.
Total HP curable with 2000MP Pool
Sub Cure4 Cure5 Cure6 Cga3/3 Cga3/4 Cga4/3 Cga4/4
Base 25000 31429 21127 45000 96000 77647 293333
Blm 28571 36066 23622 52941 126316 98507 733333
Rdm 52402 64897 42918 92545 200837 159420 633094
Sch 39600 52171 33693 82094 262400 177893 #INF
Cure 4: /rdm wins by 32%.
Cure 5: /rdm wins by 24%.
Cure 6: /rdm wins by 27%.
Curaga 3/3: /rdm wins by 13%.
Curaga 3/4: /sch wins by 31%.
Curaga 4/3: /sch wins by 12%.
Curaga 4/4: /sch wins by undefined amount (you actually gain back more MP than you spent, so you can do an infinite number of casts at this level).
So for single-target casting, /rdm wins. For multi-target casting, /sch wins. Given the scenario described in earlier posts, with large numbers of DDs on the mob, I would think that the whms would want to focus more on curagas than single-target cures, making /sch a better choice.
/sch gains a small advantage from other things being cast that don't gain the benefit of the AF3+2 pants (eg: Haste costing 36 MP instead of 40), plus the fact that it doesn't need to spend time casting Refresh. Curaga 3/3 probably ends up being about a tie between /sch and /rdm once other factors are accounted for, but /rdm should still have a 15%-20% edge with spamming Cure 5/6.
/sch has its greatest edge when using curagas on 4+ people. The flat cost reductions available to /sch, combined with AF3+2 legs, makes it so that there's almost no cost (or even an MP gain) in casting them, and they're the best spells to use for things like Gates of Hades, Acheron Flame, etc.
I've actually found that, aside from other conveniences (eg: Esuna), it's easiest for me to stand right in with the melee and spam Curaga 4 on mobs like Orthrus. Adding an extra person who took damage (me) to the cured list gives me that much more MP back, while at the same time I'll likely take less damage than anyone else anyway. If I expected to use Convert this would be a Bad Idea.
And of course if you're not actually using enough MP to require convert (such as by taking advantage of curaga efficiencies), /rdm loses its greatest advantage. For example, if you need to cure 100,000 total MP, it can't be done with one MP pool using single-target spells even for /rdm, but is easily manageable using most curagas for any sub.
If you needed to cure 60k HP, you'd want /rdm with Cure 5 since /sch couldn't manage that in one MP pool. However /rdm can't handle 70k on one pool; at that point you either need curagas or a second whm. A second whm means you're only curing 35k, using less than 10% of the Converted MP pool and swinging the advantage way back towards /sch. Curagas mean you're not needing the Converted MP pool at all, and /sch is more efficient for that.
Realistically, of course, you're going to have a mix of the two. With 3-4 Cure 5's per Curaga, advantage swings back towards /rdm. And the advantage of one or the other will swing back and forth based on exactly how much actually needs to be cured. Edited, Jun 28th 2011 4:42pm by Kinematics