You need to stop thinking that dedicated graphics are magically more performant than "integrated ones". And the Retina MacBook Pro can barely keep up because the CPUs have to suddenly decode 4x image sizes, it has little to do with the GPU. I mean, think about it, we've been able to run multi-monitor setups on the MacBook Air with far fewer pixels and that has a far weaker GPU.
Anyway, performance specs on Iris 5200 Pro:
http://www.anandtech.com/show/6993/intel-iris-pro-5200-graphics-review-core-i74950hq-tested
Basically, GPU performance is slightly weaker than a GT650M. Could they include a dedicated GPU? Maybe. But that extra $100 from the eDRAM which Intel is charging likely means no dedicated GPU. For those looking for better GPU performance, you're going to have to wait for Broadwell.