I'm rusty on the exact wording. Class III spell takes 2 rounds to prepare, 1 to cast. That is the spell caster's current level, and the next 2 levels down. So for a level 5 caster, spells at Level 5, 4, 3 are class III spells.
However, a class II spell is Caster's level - 3. Level 5 caster takes 1 round prep, 1 round to cast a level 2 spell. Firing off a spell every other round is similar to an archer getting off an arrow every other round.
At this point, the spell caster can also "hip shoot" a spell and cast it with slight penalty without full rounds of prep time. We would have spell casters in our group hip shooting Class II spells all the time. They were so good at the spells skills, the negative hardly ever impacted their casting ability. Now spell casters are getting off higher level spells, every round still at only level 4 or 5.
Spell casters also have the ability to "over charge" a spell to increase damage, duration, or other aspects of a spell.
Spell casters can be very dangerous in RM but they have to know their own limitations. Do not go into battle in the vanguard. Even while prepping a spell, the caster isn't standing still like a statue waiting to get whacked in the head. He has some movement ability and should be ducking behind cover if possible and has some DB to offset attacks from what SHOULD be other lower level characters. A level 1 mage shouldn't be fighting a level 5 fighter. IT's easy to break a caster's concentration on a spell prep... but it's also difficult to break a caster's concentration on a skill prep. (Sounds weird, I know, but it's not as easy to break a caster's concentration as it sounds.)
If the spell caster is crafted well, a level 1 mage can have access to four spell lists, additional PP if the GM allows the optional skill - Power Point Development, hopefully a background option on the Special Items category that gives a PP adder or PP multiplier, and a background option or two on the Skill at Magic table. At level 1, the mage is pretty decent.
Just remember Rule #1: Take out the spell caster first!
And of course Rule #0: Protect the spell caster first!!!