As for Head Butt, don't forget that Blue Magic accuracy is based on your main weapon rating.
The acc of physical blue spells is indeed based on weapon skill rating/physical acc. But the magic acc of the additional effect, in this case stun, is based on your blue magic skill.
So headbutt stun very very rarely lands from /blu. Also, /blu dispels aren't gonna land on anything of a high lvl.
But then again for defensive buffs I'd rather /rdm, phalanx, regen and stonekin and so as well as protects and shells. Personal prefs though, and I generally forget about prot and shell =p
Thoughts on buffs for DRG solo.
Stoneskin: SS is most useful as a pre-battle buff. And really more for the wyvern's sake than for the DRG.
In-combat DRG has serious issues successfully casting a spell as long as SS. Unless you use aquaveil too. And then there's another long casting spell eating away at your DD time.
Perhaps the biggest thing though, is that for DRG, a simple healing breath cures far more DMG than SS would prevent, and is faster, more mp efficient, and more likely to fire successfully. It's usually just not worth the time it takes to cast it.
A notable exception would be for attacks that might otherwise one-shot you. But very few of these are slow enough for you to cast SS before they fire.
Regen: I've found regen to be more annoying than helpful for serious DRG solo.
In a hard solo fight, where you're spamming HBs, it's very important to know exactly at what point(amount of HP) you can trigger a HB, and to trigger as early as possible once you can. So you're watching your hp, ready to slam your HB macro as soon as you're low enough. And you get just barely in HB range, start casting.. and your hp ticks up from regen, and knocks you out of your HB threshold...
So now you get to eat more hits, and get even lower while you wait out the cast time, and delay till you can cast again, then the delay after the next cast while HB charges.
That delay can, and eventually will, get you killed. Mind you, that's really only if you like really hard solos. And among those mostly outside abyssea. With abyssea's huge HP pools, you're very likely going to have time to try again if you miss a HB.
Phalanx: I love phalanx.. On PLD. On DRG, it's a pale shadow of what it could be. Still, it's better than it was at 75.
Lvl 47 RDM yields 138 enhancing skill. Or a -11 DMG phalanx. If you were to spec out for it, you could get 174 skill(merits and +20 in gear)for a -15 DMG phalanx.
The thing is, I'm moderately certain that for physical dmg, cocoon's +50% def is going to yield a greater degree of dmg reduction. This, of course, is going to depend on the mobs's lvl and atk, but on anything high lvl I believe cocoon will come out ahead.
Now, if you're /rdm for some other reason, by all means continue. But if the focus here is surviving heavy physical dmg, then I'd suggest getting on /blu, and using cocoon.
Aquaveil: Aquaveil is actually quite powerful. Being interrupted during solo can be deadly, and aquaveil can let you cast long spells you couldn't normally get off.
But it has two issues for DRG.
#1: the # of interrupt guards is very likely based on enhancing skill(no extensive testing that I know of). In my experience, sub skill aquaveil usually yields a single interrupt guard. Then it's gone.
#2: It has a long cast time. About the only way to cast it mid combat is to already have it up. Or to get a quick magic proc.
Basically, it's a good pre-combat buff. But that's all.
Blink: Blink, somewhat surprisingly, actually has an in-combat use. If a limited one. Against higher tier single target nukes, it's possible to start casting it when you see the nuke start, and finish before it fires. Depending on the mob's job/fast cast.
Since blink has no modifiers, and a near non-existent recast, there's no need for any specific gear when it fires. So you just start casting it, then swap in MDT for the nuke. In case blink is too slow, or the shadow fails to take it. I've also noticed that blink seems to have a much higher proc rate against spells than than melee.
Subs
/BLU: For hard fights vs hard hitting, physical DMG focused mobs. The most MP efficient sub. Cheapest triggers(5 mp), and only one 10 mp buff. Fair DD. No real bonuses to DMG output(stat boosts from spells are pitifully small) but wastes very little DD time casting.
/RDM: Greater general utility. Good vs magic using mobs, mobs with en-effects, and fights where bar elemental spells and resist builds will be useful. Very fast, cheap triggers. Has Dia II and enspells for DD, but depending on playstyle, can burn alot of DD time/mp casting extra stuff. Refresh makes up for alot of the extra MP use from all the buffs. But casting it in-combat's a pain.
/WHM: Much the same utility as /rdm. Also has -Na spells/erase for fights with nasty statuses. Haste and Dia II for DD. I would say this is currently the best offensive solo sub. But that'll change when /rdm get haste.