Here is a size comparison showing the Ambull Green next to an old Rogue Trader era Space Marine mini. I'm pretty satisfied with the scale, which is lucky because when I started the sculpt I did not pay too much attention to how big it was going to be.
This got me thinking more (for the future) about how to properly size a project before beginning. I printed out different sizes of Leonardo's Vitruvian Man to get an impression of how big or small certain scales of minis should be. Tom Meier wrote this very helpful article about this on his blog about minis and proper proportions.