Erik, I'm running a game in the late 700s - we started in 783 and after 33 sessions are now at 801.
Here are my musings from a PM I sent someone else a while back:
I didn't make a lot of changes at first because I wanted to see just how much mythic europe would change with powerful wizards using the majority of the corebook. In hindsight I should have nerfed things right out of the gate. I did nerf:
i. longevity rituals (half as effective) - most of the founders did not live very long.
ii. removed pretty much all MuVi meta magic
iii. No Stat boosting rituals for CrCo, CrMe
iv. No hermetic books since vis is so plentiful - western Europe at this point had very few literate people and book making skills are hard to come by.
v. few spells are written up, so the PCs have to invent just about anything of interest
vi. Any time a player thinks up something that is too powerful, or uses some obnoxious part of the rule set, I've nerfed it. I think it's a good policy. This is the beginning of the Order, I was very upfront with them that I would be nerfing the rules as written, but was not completely sure where I'd start.
Here's what I think definitely needs to be nerfed, possibly in addition to the above:
i.) A flat +1 or +2 magnitude to all spell levels to reflect the lack of refinement of the magic of the order of hermes. These can be removed slowly over time with major (for a form) or minor discoveries (for a technique/form combination)
ii.) No, or at least very few Major Hermetic virtues for characters not part of a mystery cult. These virtues represent a deeper understanding of the arts that just shouldn't exist in the 700s and represent various half integrated major discoveries.
iii.) throw out a few things from the range/duration/target table that don't affect iconic "magic" spells in the game. (i.e.Room as a target, diameter duration, maybe even sight range)
iv.) Most of the the various Vim spells represent a minor discovery of some sort, especially Muto Vim.