I've done this with a combat speed of 3, 3.2 and 3.4. I'm very early in the game. I'm not at home now so I can't remember the name of the spell, I think it's just called "Burn", it's the newbie spell. If attacking costs 1 and casting a spell is an attack I should only be able to cast 3 times? I can cast 4 times before my mana is gone. I can attack a group of 4 creatures and on my first turn just kill them all because my spell does 8 damage and the either have 7 or 8 hp's each.

If that is the way it's supposd to work that is fine, I just feel that it's a bit over-powered

And shooting a bow takes neither mana or moving into melee! This is why you never hear about channelers and burn spells in world history, archers were clearly superior anyway. Historically the only competitive alternative was the cavalry who can swing his sword 3x as quickly as an infantry, if he can only get into range before armor-negating bows turn him into a pincushion. Of course, then there are horse archers .. no wonder the Mongols did so well, all they had to do was move back a couple spaces before using the rest of their action points on overpowered ranged attacks.