I beleive MM6 has the best spell solutions in all the MM series. Although you could learn the spells at lower lvl you could not use them effectively because of e.g. low mana pool or simply due to GM requirements for the spell to work fine.
I almost finished MM9 with 2 offensive spells exclusively EB (way better at higher Elemental than a Bow skill, imho)and PC while in mm6 there was this nice progression:
I started with sparks; then got fireball, firering, lightning bolt; and then all the daeth spells... .
In terms of offensive spell use MM9 is kind of dissapointment for me - in mm6 there was more planning and more strategy to it, imo, and mm9 is more strightforward.
