Hans von Hammer:
Really? I've always painted X-wings overall flat white and then heavily weathered them... Never even considered them to be any shade of metalic grey or grey, other than possibly some where painted that way to match the lighting used in the FX shots...
I think that the lightest shade of grey I'd use on the T-65 would be Model Master Camouflage Grey, which is about as white as a grey can get and still be called grey.. It also helps with those red decals a LOT...
While I lost the old X-wings I built years ago during a move, I'm considering finishing a started 1:72 one from FineMolds that I got in a lot on ebay a while back. I don't know what color the instructions mention, but I was considering using FS light gray instead of Camo Gray. I figure it'll make the red and yellow decals you mentioned stand out a little more. I think the warmer Camo Gray will work better on the Falcon.
As far as the metallic option, the main shots I remember making me consider that were in the scene where Luke's climbing into his fighter to leave Hoth, where the skin didn't seem to have the same gray look as it did in the hangar scenes from Ep 4. There's a strip near the cockpit that even looks a lot like brass.