So if I wanted to use Odin, would I go for an Atk Boon or Spd Boon?

Ok, let's see here

Blade mages tend to prefer to double, and doubling is the safer option for Odin because his atk is pretty low even with a boon.

32 spd isn't fast by modern standards but he's expecting a buff because of his tome and we haven't considered his A-skill so if we say L&D (because he has easily enough bulk to take one hit) + receives hone spd + spd boon it's 44 spd which is pretty reasonable for a conventional desperation build.