Keep my 970 to go with my new 1070 or no?

[LORDPrometheus]

Currently i am using a GTX 970 for both my monitors. I am about to get a new 1070 and that will take over as my main card so now i have to make a decision. I have determined that there are three options for my old card please let me know which is best.
1: set it aside or sell it
2: keep it in to run my second display and use as a rendering card
3: keep it in as a PhysX card or later use for Asynchronous Multi GPU?

 

[Ideal Computer Education YT]

The only thing I can suggest is that Do whatever you want but don't sell it..... It can be very useful.