If you're on mobile GPU chipsets the latter is actually more common(CPU/GPU being in the same memory space).
That said it doesn't really change a whole lot, each platform has it's own unique performance characteristics and I don't think you'll ever correctly represent that at the API level. APIs tend to move much slower than the hardware platforms that power them.
That said it doesn't really change a whole lot, each platform has it's own unique performance characteristics and I don't think you'll ever correctly represent that at the API level. APIs tend to move much slower than the hardware platforms that power them.