As long as it's preinstalled it should be OK, but if you go before it's released you'll likely end up with a juicy 3-4gb patch to download, which, as our Wrinkly-butted Knight has pointed out above, would SUCK
You can now add your platform and gamertag to your profile, which will show under your name when you post (see mine).
If you want to have this information public, click on your profile at the top right, click edit profile, then add it in. Easy.