Best means of collecting wizard runes of specific levels.

[runlvlzero]

I recently started up a wiz and am obsessed with having all spells. I would like to research and do it early to raise my skill up. I have a couple questions about runes.

Now I know the standard method of scouring vendors in the various zones were they are dropped. Above and beyond the latter method I would also like to know a few things.

Can any mob above level 16 drop a rune for their level or lower?
Do animals like spiders, bears, and wisps drop runes if they are high enough? Are certain mobs or zones more likely to drop runes then words or pages?
Will a high level mob like a griffin sometimes drop runes for low level spells or always higher level runes?

Anyway any pointers, tips, or answers to the above questions would be much appreciated. I have already managed to compile a list of spell recipes and have found some of the spells I need to research on other vendors.

Thanks in advance. Your friendly nooby wiz.