Nice improvement Tob.
I don't know much about the rendering process in Blender, but one thing I would try is to look for a way to control the specularity with a texture map.
In Keyshot, for example, specularity is controlled with a greyscale texture file, in exactly the same way as GP4.
This might help with your reflection issues.
I'd also suggest using a texture without the shadings on it, and rather let Blender do them. (Though this will of course affect render times)
And, of course, with this model and others, you're limited by the process used to get it GP4-ready.
The way that Zmodeler (and I think the .gp4 format itself) handles smoothing groups really badly affects any model that goes through it.
Again, really good work.
(I tried Blender for renders once upon a time, and gave up after about an hour of getting nowwhere!)
F1 Graphics Swapper ---
Lensdump - Renders and Screenshots ---
GP4 Performance Generator