See this page for details of what the GPU is used for in After Effects:
See this page for benchmark results of various cards used in GPU acceleration of the ray-traced 3D renderer:
thank u very much for this info
Forget about the Quadro FX 5600: That GPU is severely outdated now, being a full six years old now. In fact, its age goes way, way back to the very first generation of CUDA GeForce GPUs (in this case, the GeForce 8800 Ultra). Worse, you cannot enable CUDA MPE GPU acceleration at all with that FX 5600 (and thus Premiere Pro MPE will be permanently stuck in the software-only mode) because the compute capability version of the FX 5600 (like all other GPUs using the G80 core) is only 1.0. MPE GPU acceleration requires the compute capability version number to be 1.1 or higher to even enable GPU acceleration at all.
In addition, the Mac Pro 3.1 is almost equally, if not more, outdated than the Quadro FX 5600: It is based on a pre-Nehalem CPU - a CPU that's based on a 45nm die shrink of the Core 2 Quad. As such, it has no L3 cache and its memory controller is external (on the motherboard instead of on the CPU). And it uses the now-long-obsolete DDR2 RAM instead of the DDR3 RAM that current systems use. As a result, with such an ancient platform (fully five years old as of this posting) and even with the fastest GPU and disks, the performance ranking would still fall below Q1 (first quartile). More likely in the middle of the D1 (first decile) range.