[Radek]

As far as the boogres are concerned, think twice what is more worth for you. Either the 100 HP or the fact that:
a) Boogres are SLOW. Very slow!
b) The hihger level spells cast by boogres do fail. You will have no problems with level 1 - 4 spells. Level 5 spells fail only seldom. Level 6 spells fail more often. Level 7 spells fail in about 40% of cases.

Therefore, the boogre mage will do well - as long as you will want him to cast only low level spells. But prepare for problems if you are relying on level 6 and 7 spells, like Incinerate, Restore Health, Firestorm, Meteorstorm and so on. Don't forget Murphy's Laws. The spells will fail in the moment when the failure is most unwelcome. Also, you'd better save the game before casting Create Portal, Teleport and Call of Home.