4GB is plenty of memory. I was hoping for 2GB from the new generation. People complain about long load times now when they just have to fill 512MB of memory, get ready for load times 8 times as long (or will they have and SSD instead of a regular hard drive?).
The GPU is vastly different situation compared to a PC. In a console programmers get up close to the hardware but in windows the APIs can make things 5-10 times as slow depending on what you are trying to accomplish. You are forced to program for many different architectures and so you go through the layers of generalization which can cost you huge depending on the actual function of course.