Whatever you do I'd do it soon! You're thinning quite bad and it's only going to get worse the longer you leave it.

Also, when you order your full or almost full cap just be sure not to overdo the density! Go low density, but just a bit more than you have already. Since everyone is already used to seeing it that way, it won't be that surprising when you have just a little bit more.

If you go too dense it will be obvious. You can build up the density a bit with each progressive piece. You can even just tell everyone you're using minoxidil or propecia.

Also keep in mind with a full cap (as with any piece) it is easiest to pull off with a hidden hairline.

eg. Jrob style:
http://hairjive.com/blog/