Overkill

No it would not. You're not paying a premium for the BE of the cpu. There is no standard 955 model. The next lower model is the 945 non BE which is 10 dollars cheaper and 200mhz slower. The only way it will be a waste of anything is if the computer will not be doing anything that will benefit from the quad core.
 
I have a 955BE.
A friend has a 956BE.
Another friend has a i920.

TBH, I wouldnt change my CPU at all.

Video editing, Gaming and Rendering.
Price vs Performance, I love it.

Dave