B/X: High Level Spells

A commonly known quirk of the B/X system is that the game only goes up to 14th level. This means that clerics top out at 5th level spells, and magic-users at 6th level spells.

I love the experience level cap in B/X, but I'm kind of ambivalent about the cap on spell levels. I love me some spells (especially magic-user ones), and there are indubitably some very cool spells at 7th, 8th, and 9th level. We probably all have books full of them.

So I've been thinking for a while about a way to (potentially) bring the higher level spells into B/X, without increasing the maximum level attainable by magic-users. Here's one idea. (Not tested in play.)

High Level Spells (Optional Rule)A magic-user of 11th level or higher is able to cast spells of 7th, 8th, and 9th level.

Acquiring High Level SpellsSpells of 7th, 8th, and 9th level may be added to a magic-user's spell book by the following means:The normal spell research procedure (see B/X Essentials: Core Rules, p31 ).By studying the description of the spell in another magic-user's spell book (using read magic). This takes half as much time and money as spell research (i.e. 500gp and one week per level of the spell).
Maximum High Level SpellsEach magic-user may have at most two 7th level, two 8th level, and one 9th level spell in his or her spell book.
Casting High Level SpellsSpells of 7th, 8th, or 9th level cannot be memorized. This means that, while a character may have such spells in his or her spell book, they cannot be cast in the same way as spells of lower levels. High level spells may only be cast as follows:A special ritual chamber is required. This must be constructed as part of the magic-user's stronghold (upon reaching 11th level or higher). It is not possible to cast spells in the ritual chamber of another magic-user.Each time the spell is cast, 500gp worth of rare ingredients per level of the spell are consumed. The magic-user must acquire these ingredients before casting the spell. (The referee may wish to specify the nature of these ingredients, possibly tailored to the nature of the spell to be cast.)Casting the spell also requires time: 1 hour for a 7th level spell, 4 hours for an 8th level spell, and 8 hours for a 9th level spell. If the magic-user is disturbed during this time, the casting of the spell fails.At the culmination of the ritual, the magic-user may choose how the spell manifests, selecting one of the following options:The spell takes effect immediately.The spell's effect is woven into a staff. At any time in the future, the magic-user (and the magic-user alone!) may break the staff, releasing the stored spell effect. The magic-user may only have a single staff enchanted with a high level spell at any one time.