You could sit on it and use it as an uptrade on a future engagement ring. I did that for the wifey when I got her ring, jewler had no problem putting the orignal purchace price to the new ring, as long as I went at least 20% over the original rings price.
At the same time, that is a lot of money sitting there. At least with the value of precious metals rising against our somewhat weaker dollar, you have a set comodity that is holding value.
BTW, the wife said she would kill me if I bought that for her, she wants a CTS.
Good luck with the sale.