Each time Sublimation ticks, it calculates the maximum charge based on your current stats and checks it against the current charge and your current HP. In theory, you could calculate the exact number at which you switch to max HP gear, but in practice it's pretty difficult. For one, it's very difficult to tell exactly how much MP you've stored at any given time, unless you fulltime Scholar's M.Board and/or Argute Gown, which isn't really an option.
Also, unless you're using Spellcast, you'd need another macro to equip that max HP build to make it work, and macro space is scarce and valuable for SCH. To each their own of course, but squeezing another 30 MP into my max Sublimation charge isn't worth giving up the macro space.
However, I do make use of a max Sublimation set; it just equips all the HP+ i have, plus a few things like Bomb Queen Ring that I keep in my Satchel. I don't use it in everyday situations, but it's pretty useful when I have time to sit around and build up a maximum charge before engaging, like before I enter a solo Limbus run.
Concerning Sublimation eating away at Stoneskin, Auto-Regen goes a long way towards reducing wear and tear on your buffs. Assuming Scholar's Mortarboard 3/tick Sublimation, add Orochi Nodowa; a 300 MP charge only eats 200 off your Stoneskin. Add Garden Bangles w/latent active for 300MP:100HP; and if you have an Ixion Cloak, you'll have 2/tick Sublimation, 1/tick Auto-Refresh, and at worst 0 lost HP, at best 1/tick Auto-Regen.
There's a lot of talk on the boards as to which combination of gear gets the most efficiency out of Sublimation, but that's just numbers on paper. If I'm in a situation where I know I'm more than likely going to be taking substantial damage, I use Ixion Cloak. Sure, my MP efficiency goes down slightly from Scholar's Mortarboard, but my survivability goes up considerably as I won't have half-worn Stoneskins protecting me. I'd rather be alive with an empty MP pool than dead and unable to cast anything.
Edit: I was mistaken on the above two points; the only way Ixion Cloak increases survivability is by lowering the HP dealt to your Stoneskin; not as impressive as I stated initially!
Edited, Aug 4th 2009 9:21pm by LyltiaofLakshmi
RDM can attain an almost static 50% reduction to recast time, SCH can over shoot this for a total of 60% reduction under Alacrity (provided you are wearing loafers and keeping dark weather on yourself)
MACC is a joke, any job with access to mage gear can hit close the MACC cap on legion mobs, which is why my BRD/RDM can land slow/para/blind despite having only 150 skill (from /RDM.)