7970m vs. 980m

Hi everyone.

I have a question. I currently use a Radeon 7970m in my laptop, and am considering upgrading to an Nvidia 980m. It will cost around $1000 to upgrade, and I'm wondering if it's really going to be worth it. What do you guys think? How much more performance exactly should I expect to see? Any tips or pointers greatly appreciated as I try to make up my mind to take the dive of upgrading here. Thanks!