If scaling with Cadians, it's the proportions and bulk rather than the height that I think is the big factor.
To that end, the Stargrave plastics are one of the best options. They are a mm or two shorter to the eyeline, but the proportions are dead-on for GW-chunk.
In fact, alot of the figures sculpted by Mark Copplestone (who also did much of the Stargrave metals I think...) will have similar heft. Copplestone castings and EM4 (formerly Grenadier) Future warriors figures will look pretty good with them.
I'll think on what else I've got and what else might be compatible...