The 50% EQM rule will likely be your deciding factor.

CO only awards 50% EQM on cheaper fares on NW/DL/partners. CO awards 50% EQM on its own cheap fares, unless purchased on its website.

So your travel patterns, as well as buying habits will factor into this.

If you buy discounted tickets, and you are able to buy those tickets at CO's website, then there may be an impetus for you to change to the CO program.

If you do not buy discount tickets and/or may not buy tickets at co.com, you likely will be in the same boat, so it's not worth switching.

Now with all that said, if you have status with NW and want to switch, CO will likely not match it, as they are partners. So it would actually be easier for you to switch to a different alliance than to switch to a different carrier within the same alliance. It kind of doesn't make sense, and I wish they would consider external factors (such as moving) into comp requests, but it may be easier for you to switch to AA or someone instead of CO. Go figure.