Very nice, to me at least these images looks much better and interesting than the first ones you posted. I still think you should try HDR lighting, simply to get those reflections into the scene and maybe an ice ground for it to sit on again just to further expand it. The last 3 image looks nice I think, despite being in a dull gray environment, and even though the last one with emission added, might not work in all environments and I think you could achieve the same effect simply using a "correct" light setup in your scene, its looks very cool.

In regards to pixel samples I don't think that 50 is all that much to be honest, a cheap trick is to render slightly larger than your final image and then scale it down, since that will force it to compact the pixel a bit and can therefore reduce the noise, but it can reduce the number of pixel samples needed slightly, whether its worth it or not depends, as it will reduce overall quality slightly. Also you could try to scale it and rotate it and place more of them inside each other to see if that give some more depth and effect to the ice.