You might be able to make those max magnitude spells, but casting them is a wholly different story. At level 5, I doubt you can actually cast them. Make spells that you can cast, and when you have reached a higher level in the associated magic skill, then make the uber spells.
Oh, for sure, I don't expect to be able to cast them at max duration now.
I am very surprised that duration can't increase past 2 mins. I suppose recasting has to be the solution here.
I'm sure I've seen other spells (and maybe scrolls) with durations longer than 120 though.
As far as removing spells, can someone else confirm or deny this?
Not being able to remove spells was also an issue in Morrowind as I recall and, again, I'll be surprised if Beth didn't fix it in Oblivion.
Maybe there's a mod, or save-game editor somewhere? Surely someone has to have thought of it.
-WSCraft