I would go for a higher number something between 49152 up to 65535...
From what I can see from the screen shot of your router you still have two different numbers there...
I will give you the instructions for a different Westell model (I can't find any for the one you are using) It suggests to do a static IP, I just assumed that you had already done this as you mentioned port forwarding for your xbox...If you have never set up a static IP for your computer you will have to do this step, you only have to do this just the once...
These instructions also show you how to do that, although there not the ones for your router they will give you an idea of what the process is...
Port Forwarding for the Westell A90-327W15-06