Upgrade availability on this route can be scant and you should take it when it is available. As a silver, your op-up chances aren't that bright considering that there are usually between 15-20golds on this route in Y.

One other factor you may want to consider is when are your miles expiring. If they are expiring soon and you don't have any trips planned before them (and there is no guarantee that you may be able to use them for an upgrade then as seats might not be available.), go ahead and use them to snag the upgrade. Using miles on the Emirates high Street is the worst use of miles and it'll pain you why didn't use them for the upgrade....