I noticed that you are having issues with the frame rate of your Slingbox while using the SlingPlayer for Boxee Box. Unfortunately, Watch on Slingbox.com does not have the option to change those parameters. If you lowered the resolution and the issue persists, this problem can be caused by the firmware on both devices. Make sure those are up to date.
Use the following link as a guide for the troubleshooting:
I hope that helps. Regards!
I'm having a similar issue with my Boxee. On the same network, if I use the Watch on Slingbox.com and use the Best/HD mode, the frame rate and sound is very fluid (almost HD), however, when i select the same on boxee, it stutters and I have to switch to better (not nearly as good). Is there a resolution for this or are there different modes supported by Watch but not Connected Devices? My computer is a 1366x768 screen and my Boxee is attached to a 720p TV.