I'd have gotten a mirror quickly if I was staying in the states for a while and verify the quality of the mirror first.
Discovery mirrors are about as good as the others (I live near them and have seen a few of them as a result as local purchases tend to be a bit more frequent with any company - you can just go to the shop and pick it up there instead of all the shipping charges. The mirrors have all been decent ones that I've seen but nothing really outstanding for shape.
The coating reflectance really isn't all that great so, while you may see a little more, the differences won't be that large even for an experienced viewer. I'd not worry about getting any of the advanced coatings as a result.
This is probably your first scope and you want everything to be perfect but you have to remember that you can get more performance out of a slightly larger mirror than a better coating on the smaller one. Besides, the scope won't be the only one that you will ever own and, in addition, there is no perfect scope. Go buy one of the size you want and enjoy what it does do.