As I've said before, the D&D wizard is my default image--though I can't quite put my finger on the reason. Like you, I read LotR long before I became acquainted with D&D, but Gandalf...I think he got associated with an entirely different word. Or a concept that can't be described in words. Gandalf is...you know. The "wise man." The original meaning of the word "wizard," which had become disassociated from it in my mind. In this way, he's more closely associated with Indonesian legends about wise, mysterious clerics like the nine legendary preachers who are said to have played crucial roles in the spread of Islam into Java. Weird isn't it?

The D&D separation between Int and Wis has also been a puzzle for me. But then, maybe it draws on a different archetype--say, the maddened "wizards" we see in things like Faust or Lord Byron's works. More like Jonathan Strange or Gilbert Norrell than Merlin or Gandalf, in fact.