Well, the half sovereign is probably not likely to go up much in premiums, it has had many years to appreciate and the price you are paying above spot today is probably not likely to change much.
The 10oz bullion though, if it is a Perth Mint coin from a few years back before the milk spotting, and it is in good condition, it might continue to appreciate in value. Particularly if it is part of an ongoing series. People who have collected the 1oz series might go back and collect the other sizes. If it was a Dragon then I would say no contest, if it was one of the lame koalas then maybe not so much.
But I like silver and I like having a large lump of metal for my money. If I had to flee the country or I was collecting gold coins I might get the 1/2 sov.
