.999, .925 or even .500??

Hi, I have been stacking .999 rounds and bars for the last year and have a bit now. I was just wondering what peoples thoughts are on the .925 (pre 1920) and .500 (pre 1947) UK coins i have looked on the bay and you pay less premiums on the <1920 and far less on the <1947. I was wondering what peoples thoughts on reselling the .500 when the prices go much higher. Will there be huge demand for .500 or will it be seen as real junk, as .500 is very very cheap per 1 oz pure silver quantity.