While finalizing the text of the upcoming 2nd edition of the Hungarian retro-clone Kazamaták és Kompániák, we took a look at clerics. Here's a simple table that sums up XP requirements and spells/day by edition (note that it's an incomplete table; Rules Cyclopedia, although up until level 14 matches Mentzer, grows way beyond that, and so does AD&D). I'm specifically looking at 3rd, 4th, and 5th level spells to gauge power levels. For reference, among others, consider the following spells:
- 3rd level: Continual Light, Cure Disease, Locate Object, Remove Curse
- 4th level: Neutralize Poison, Protection from Evil 10' radius
- 5th level: Commune, Quest, Raise Dead
When you consider that clerics gain access to all the spells on their list (except in AD&D, where 5th spell level and up are provided directly by the cleric's deity), and the fact that the spell list grows a little bit in each edition (for instance, Mentzer adds Cure Blindness as a 3rd level spell and Dispel Magic as a 4th level spell to the cleric's repertoire), you can see the power discrepancy between the editions.
As noted on the summary sheet, a Cook/Marsh cleric gets access to 4th and 5th level spells at level 6 (i.e. 25,000 XP), whereas a magic-user in the same edition only gains 3rd level spells at level 5 (i.e. 20,000 XP). By the time the magic-user gets their first 4th level spell at level 7 (i.e. 80,000 XP), the cleric has already got access to 5th level spells (from 50,000 XP, actually).
In Mentzer (and the Rules Cyclopedia), however, the clerics' power curve is steeper. They only get their hands on 4th level spells at level 8 (i.e. 100,000 XP) and 5th level spells at level 10 (i.e. 300,000 XP), which is comparable to magic-users in this edition (level 7 and 9, i.e. 80,000 XP and 300,000 XP, respectively). Furthermore, for an extra set of 6th level spells, clerics in Mentzer can cast fewer low level spells at the highest levels (although in the Rules Cyclopedia they make up for it as they advance beyond level 14).
AD&D is somewhere between the two B/X editions, with the caveat that clerics have access to 1st levels spells from level 1. They get their 3rd level spells the quickest (at level 3, i.e. 13,001 XP). They receive 4th level spells at level 7 (i.e. 55,001 XP), which is comparable to magic-users (level 7, i.e. 60,001 XP). In fact, magic-users get access to 5th level spells sooner than clerics (135,001 XP vs. 225,001 XP).
Even though the cleric's spell per level table in Cook/Marsh hurts my sense of symmetry, it allows the proliferation of save or die effects. If you think about it, if a party of six acquires a total of 300,000 gp during their adventures (and that's without XP for killing monsters!), their cleric gets access to raise dead - for the same to happen in Mentzer, those 300,000 gold pieces must have been acquired by the cleric alone.