I know this is an old thread but reading through there is some misinformation listed. The rarest caliber gun combination is the pre 64 model 70 .308 in STANDARD grade. I had an opportunity to purchase one back in the 80's new in box for $5,000.00. I believe it is worth around 10 times that amount today NIB. The .308 was only cataloged in the featherweight model 70.
Very, very unlikely that anyone would ever pay $50,000.00 for a NIB 308 Standard Rifle. Where did that number come from? Winchester also cataloged the 308 in the Super Grade Fwt configuration....