The PS4 actually has a GPU with a performance level that sits in between a 7850 and 7870. Not the highest end GPU out there, but consoles have an optimization advantage vs PC, so you generally need a bit beefier GPU to get the same results.
On the other hand, the GTX 780M is one of the most expensive single GPUs you can buy. It's a GK104 Kepler core with 1536 CUDA cores, similar to what we see in desktop products like the GTX GTX 680 or GTX 770.... only, it's one that has great binning for lower voltage use, and is running at lower clockspeed, to stay in reasonable thermals.
- Performance is about 20% less than a GTX 680, which puts it's desktop equivalent around... well, somewhere between a 7950 and 7970 if we tried to compare vs...