Both graphics cards are comparable in performance.
I would not plan on dual cards as an upgrade path so long as there is a stronger single card that will do the job.
What is the rest of your pc?
For a similar price, I would opt for a GTX970 card.
It is a more modern card and needs less power.
For a lesser price, 2gb of vram should not be an issue.
Read this.
https://www.pugetsystems.com/labs/articles/Video-Card-Performance-2GB-vs-4GB-Memory-154/