In my personal opinion this would seem about right. On my system at home I was recently using the GTX-470 ( the minimum recommended card for use with the engine from NVidia) and I was seeing roughly the same FPS if not lower in some circumstances, on basic maps and the starter maps. I’ve recently upgraded my GPU to the GTX-750-TI and noticed a significant increase in FPS.
The 6870 is the lowest recommended card for Radeon.
If you’re looking to do large open levels I would suggest a possible upgrade or more aggressively using Culling volumes and level streaming for your terrains as Fighter5347 suggested.
You can also check the Feedback for Epic section of the forums where users are posting their Hardware and the results they are getting.
You also have the option of using the engine scalability settings (Mid-way down the page) in the viewport to achieve better FPS as well while you’re working.
If you have any other questions feel free to ask!