There is no problem with the GPU itself, it's fine. It's an issue in OS X and the immature scaling system they're using is just not fast enough, it's still demanding too much from CPU/GPUs at the moment (the hardware is capable but the code itself isn't optimized for those hardware).
This is the first time Apple has enabled such scaling system in OS X with a Retina display, so there'll be issues and it'll take several months to optimize it.
They're already improving in each software update with better drivers.
If you can wait to get the rMBP next year and you're happy with your current system, then wait it out. It'll be much stable next year with further improvements to both the rMBP but most importantly, an optimized OS for the Retina displays.