Developers have said the consoles are basically equal in power.
Gddr5 ram only gives an advantage to the gpu. The gpu stores textures, at best the gddr5 will allow extra textural, less loading, larger draw distances, ect. It is nothing that will make the games drastically different on either system. Also xbox is rumord to have some extra high bandwidth ram in order to help with the bandwidth issues of gddr3. Now where the surprise will come in is how the ps4 CPU will perform with the gddr8 ram. Current computer systems don't use gddr8 for the CPU due to latency issues, so it will be intresting to see how the ps4 CPU handles that.