The GR8's are indeed plastic I believe. Wow the sound on these is incredible. I will reserve judgement on the durability of these until I've had theme for a few months. Bass is impressive for a single armature. Mids are definitely very strong/forward and very very nice in these. I would be interested in hearing the GR10, but the durability has to be proven to me first. No response from Grado on out of warranty repairs. Cable has same feel as my 'kevlar' ie7's the stress reliefs on the monitors themselves is questionable, and I HATE straight jacks. If these can hold up for me I will purchase the GR10's eventually. Sound-wise, these are really fantastic IEM's . A little less sensitive than I would like, but we are going to be spending some quality time together.
Some tracks are harsh, isolation better than expected, vocals are as lifelike as I've heard. Very impressive.