the nice thing about IB (amongst other nice things) is that when i get stuck with an odd lot fill, i can usually autoex TMBR at the NBBO...(for nazcrack)
you can throw odd lot limit orders at specialists, too, at the NBBO (or so it seems, but i've only done this maybe 5 times in my life) so i don't think you'd ever see a difference in fill when you trade stock in odd lots...