Gishes and/or Dual-Progression Casters vs. regular Full Casters at high levels

[Schattenbach]

I'm curious about at what point or around what level would Gishes (as well as any kind of build that has considerable physical combat capabilities as well as considerable spellcastng capabilities) and/or Dual Progression Casting Builds (Theurges, Ultimate Magi, etc.) actually catch up or even surpass regular full casters and might thus actually be an at least slightly better (or even outright superior) choice? After all, expect for fewer feats invested in actual spellcasting capabilities/fewer dips in powerful casting PrCs/likely being MAD/likely slightly behind in caster level, once 9th level spells (and, possibly, epic spellcasting) is there, there isn't that much of an downside expect for facing more harship until finally reaching that point due to being a few caster levels behind, but once those things are there, there should only be minor disadvantages (depending on the actual character makeup) at worst as far as actual spellcasting capabilities are concerned.

So it would be helpful if some of the playgrounders have time to share their opinion about this matter.

Thanks in advance.

[Eldariel]

Well. It depends on the full casters. Something like Dweomerkeeper, Halruaan Elder, Red Wizard, Incantatrix, Planar Shepherd, Hathran, Tainted Sorcerer, Tainted Scholar, Spelldancer, etc. gives abilities far above and beyond what the core class would allow. Thus, a full caster built with the powerful casting PRCs is likely something a gish/multiclass caster can never catch up to since the multiclass caster's character levels fall into taking a combination PRC, which has no special abilities. It's worth noting that Gishes' only class-based advantage is dead magic zones/antimagic fields: a full caster literally just needs to persist Divine Power (accessible through any number of means) to have BAB = HD all day. Well, aside from Ruby Knight Vindicators: those guys mean business. Far as caster/caster multiclasses go, it's worth singling out Ultimate Magus with its rather powerful metamagic options and the ability to cheese the caster level of its "main" class by having both sides advance it.

If we're comparing the classes to a regular Wizard/Cleric/Druid/Archivist/Sha'ir/etc. 20 with no PRCs, the easy answer is "When they get 9th level spells they're even". Combination casters are generally going to pull slightly ahead with double 9s - while single class casters have tricks to replicate spells from the secondary class, something like a 9/9 Arcane + Psionic has action economy breaking stuff far above and beyond that of a single-classed character. However, it's not completely irrelevant that a level 20 caster has way more 9th level slots innately available. Stats and items do add a lot to it, but the slots are still ultimately restrictive, so a level 17 caster isn't quite as good as a level 20 caster in spite of both having access to 9s.

Much also depends on the level of RAW available. I.a. Shapechange/Polymorph-effects granting innate casting (as a natural ability) make all the multiclass casting stuff more or less moot as you can just use Shapechange to access any spell list you want. Without such tricks, accessing other lists takes some effort giving the multiclass caster at least some tools the singleclass caster doesn't have.

[sleepyphoenixx]

It depends on the classes used. Also if you allow early entry and if the pure caster is a persistomancer.

I'd say a Swiftblade pulls at least even with anything but a persistomancer when you get Perpetual Options, because an extra standard action every round is just that strong.
Not to mention the countless defensive benefits you get out of a single 3rd level slot that you get quickened for free. Notably the 50% miss chance against both spells and normal attacks that isn't pierced by True Seeing, and Freedom of Movement is always useful.

An arcane/psionic theurge pulls even pretty quickly too if you use Ardent or early entry. The extra actions you can squeeze out of psionics alone make being "only" on par with sorcerer progression more than worth it. Throw in stuff like the Psicrystal & Share Pain combo, Temporal Acceleration at 6th level (and auto-quickened) instead of 9th and the various other psionic powers that there's no magical equivalent for and you have a pretty potent combo. Again outshined by a persistomancer, but not much else.

An Arcane Hierophant doesn't offer too much at first glance, but the advantage of an intelligent companion that's almost on par with another PC shouldn't be underestimated. It's almost like getting Leadership.
Not to mention that there's potential for quite a few nasty spell combinations. Share Spells on a Companion Familiar is a lot more potent than on a normal familiar.
There's also the all-day benefits of Wild Shape to consider. Defensive, mobility and utility that doesn't cost you any spell slots and surpasses spell-based options until high level anyway.
With early entry it's again a pretty big advantage over anything but free persist or the other "big" arcane PrCs like IotSV or Shadowcraft Mage.

I think you can see the theme here - anything that screws the action economy in your favor and/or uses early entry is about even with anything but a persistomancer.
Early entry psionic theurges are generally superior to most single-class PrCs, with the exception of the most powerful.
Most gishes won't catch up at all. Even getting to full 20 level casting sometime in epic won't make up for the sacrifices compared to a normal caster (MAD, caster PrC abilities you don't have, feats "wasted" on melee).