Due to the Slingbox video resolution, it does not matter if you get a higher connection speed. The SlingPlayer will adjust its settings according to certain circumstances. I encourage you to play around with the SlingPlayer Zoom control settings in order to get the best of your Slingbox.
I encourage you to check this link in order to know where to locate the Zoom control settings on your Slingbox:
If by any reason you are using the SlingPlayer software, this article might be useful:
Hope this helps.