Would you allow the ReVi guideline "Sustain or suppress a spell cast by another with level less than or equal to half the (level + 5 magnitudes) of the Vim spell." to affect your own casting as well? While less effective all in all, you'd only have to learn one spell.
By RAW, no. By houserule, yes.
EDIT - although it does seem that, for low-level spells (especially if you're using it in conjunction with an Arcane Tunnel to reduce the magnitudes for Range for the target spell), it's actually more efficient to use the "other" style.
ie, "Maintain the Demanding Spell" - ReVi 10 - maintains a lvl 10 spell for a diameter.
"Maintain someone else's demanding spell" - ReVi 5 - Maintains someone else's lvl 10 spell for a diameter.
By searching this very forum I have found examples to modified 'Maintaining the Demanding Spell' and I also allow it with house rule.
Changing the spell to Circle, Ring allowing localized protection in a Covenant
If I remember correctly it was used for ReHe marionette guards
Creating a magic item where the magic item maintained the concentration for the Mage with the 'Maintaining the Demanding Spell' infused.
This was even more powerful as the Spell in the magic item was designed with Concentration duration and the item maintained the Concentration.
In my story the mages also found/inherited one from an archmage in (almost) eternal twilight.
Yup, that's the weirdness of the math used in the formulas. They're equal when it comes to level 15 spells, beyond that the version affecting only your own spellcasting becomes more efficient.
Those +10 levels weren't all errat'ed into +2 magnitude?
It's already in magnitudes to begin with. The "problem" is:
Own spellcasting up to (level + 2 magnitudes).
Other spellcasting up to half of (level + 5 magnitudes).
Base 3 maintains your own level 5 spells, Base 1 does so for others. Base 4 maintains your own level 10 spells, Base 3 does so for others. Base 5 maintains your own level 15 spells, Base 5 does so for others. Base 10 maintains your own level 20 spells, Base 15 does so for others.
Yes, but in my eyes that is not a problem but a feature.
I misunderstood what you said, and thought the problem was like the +10 levels PeVi debate which IIRC has been resolved through errata.
Well then, to reiterate the opening question (which has so far only been addressed once actually):
If you are casting spontaneously, this answers is no obstacle (just cast the other one).
If you are casting formulaic spell, you just had to design both spells if you could feel like needing both.
It's as in the spell with the guideline: "kill a human". I would not allow the player to use it to hurt and not kill.
This is, to my knowledge, the only time in the rules that there is a specific split between "your" and "others'" spellcasting, as opposed to "your" and "all" spellcasting. Just found this odd...