Photo Trekker AW II vs Pro Trekker AW II Backpacks?

[6Speed]

For the Lowepro packs...I've looked at the specs and it seems the Pro is a few inches bigger and has removable pouches on the sides, but other than that I can't determine the difference that justifies $100 more price tag over the regular Photo Trekker.

Has anyone compared them side by side? Or maybe used both?

thanks