You will gain almost nothing by moving the engine that little.

As Mike said, extra weight is a better friend of your plane than any unbalance.

Just in a loop or tight turn, your plane will weight much more than what the static balance shows,.......and will still fly.

Per angle of banking, the wing loading due to centrifugal force (virtual weight of the model) increases as follows:
For a 20 degree bank the force increases in 6%
For a 30 degree bank the force increases in 15%
For a 40 degree bank the force increases in 30%
For a 50 degree bank the force increases in 56%
For a 60 degree bank the force increases in 200%
For a 70 degree bank the force increases in 294%

Easily, your plane can weight three times more during a bank of 70 degree!

Consider this:

http://www.rcuniverse.com/forum/fb.asp?m=10890949