I painted one up about a year ago, it's the appropriate scale for
40k, maybe a tiny bit bigger, but not easily noticeable. The mechanical component is on the large side, but you can get it on a 40mm base if you're creative.
Here's a blog on Dakka (not mine!) that has, in the 4th post, a Steamborg Executioner next to a Games Workshop Vostroyan.
FWIW, Vostroyans are a tiny bit smaller in scale than Cadians and Catachans.
http://www.dakkadakka.com/dakkaforum/posts/list/285416.page