For performance, you can watch YT videos of Windows laptops running Skylake and testing games using the iGPU.
As Apple uses the "Pro" versions of the iGPU, you can expect maybe 5 more fps?
The CPU increase isn't ground breaking, just the same 5-10% improvement.
The most interesting question is "Will Apple upgrade to TB3/USB Type C?", potentially breaking miniDisplay/TB 2 adapters. Since Apple never seems to add more ports nowadays, just removing them for the sake of being skinny.
I'm hoping as well for updated rMBP in the upcoming March event or WWDC. Don't want to spend too much on relatively "old" tech in the current rMBP.