Here's something I did in late 2013 for a modeling challenge (HCR #39) over at CGTalk and to familiarize myself with ZBrush's hardsurface capabilities back then, a long time before ZModeler. I pretty much used the techniques shown by Mike Jensen in his Eat3D Hardsurface DVD's (still highly recommended, btw, even now), with a little of my own twists here and there. The model was 99% done in ZBrush with that 1% being cleanup of messed up topology in Maya.
This was the status-quo at the end of the challenge deadline with ZB's soldier ztl by Ryan Kingslien as a scale reference:
Here are a few images illustrating the process I went through:
Pre-Dynamesh silhouette block-in from Zspheres and AdaptiveSkin:
Yep, that's the one. Since it was pretty much all done in ZB, I felt I should post it here, plus I'm hoping to finish this rather sooner than later, then rig and animate it. The new tools in r7 should help a lot to speed the modeling along, particularly of the interior frame. What little there is already of the latter needs to be reworked as well.
I like your choice for the current HCM, btw. If I had some time, I'd participate with a pre-AD Centurion or Praetorian. Good luck with that challenge!