get a higher end discrete card. the a10 + the 6670 is on the level of an 7770, or even an 7750 in some games. the hd 7790 would crush the dual graphics solution
Discrete card will have a much better performance than running in dual graphics .
You can easily get a R9 270 which is much faster than 7790. A r9 270 is the rebrand of a 7870..
http://pcpartpicker.com/part/powercolor-video-card-axr92702gbd5tdheoc
Going to get R9 270 from Newegg, will there be a bottleneck?
A slight bottleneck but may not be noticeable. You may suffer performance in cpu intensive games but you would probably use 85-95% of your card potential performance .