I don't know about RMC but, AFAIK, RM2's RAW don't allow casting spells without preparation so, if one goes against the RAW, when it comes to spells, ESF rules apply. Then, as stated in the ESF chapter, one round less of preparation is a +25 ESF modification whilst two rounds less is a +50 ESF modification.
That being said, the rarely used RoCo. VI offers the optional rule, in order to cast spell faster, to base spells' classes on the level a caster knows the list (rather than his own level) and to increase said level for a given casting by the number of additional PPs spent.
E.g. Level 8 character knowing spell list at level 10:
--> RAW: spells of level 2 or less are class I (8 - 6),
--> RoCo. VI option: spells of level 4 or less are class I (10 - 6),
--> RoCo. VI option 2: if 8 PPs are spent on a level 6 spell (6 PPs + 2 to speed it up), it becomes a class I spell (class I spell's level of 4 + 2 PPs expended to speed it up = 6, the level of the spell).