You'll never keep up with Cisco Linksys changes. They should fix issues, but they don't just come out with the same type of network gear except for changes and features. Looking at the new specs EA6700 I am sure there'll be EA7000 our complete change of the model name soon.
To answer you second question read the charts here on SNB for your answers. Or check with the threads for the two models your interested in. We all have opinions on which model would better.