Sometimes its not necessarily about how fast you can spam things over time, but rather how fast you can get off that one single important spell when you need it asap. Spell speed helps there.

On the other hand, determination is not as helpful as people think. It takes about 5 determination to equal 1 mind, which is approximately +1.5hp on a cure spell. Then you also have to sometimes deal with overheals which completely negate bigger cures.

I still maintain that it's a wash either way because each is so minor, so pick your preference. The number 1 thing is still getting your weapon damage and mind up first. Never pick a secondary stat over those.