This is an example scene that you can build, cusomize (or rent). The rocky islands are 256M from the lighthouse.
And my camera is also 256M from the lighthouse. The entrire space - is 512M in diameter.
And that is your editing space. You can even go out another 128m using the same techniques
you've seen with the off-sim rocks with swirling foam. And the acutal skybox in SL space is 64m x 64m x 64m. When you leave the skybox the scene vanishes and will appear when you enter it.
This is a squence of shots to illustrate the size of this scene.