The Benchmark is NOT cpu limited, it is scripted and has the same characters and battles each time.
The game IS cpu limited, especially around aetheryte plaza's and hunts (more so when occlusion culling is disabled.)
Your results are within the margin of error considering hunts and zone population can change momentarily.
after a patch and you run through gridania or limsa, you'll get full fps
as people log back in, more effects need to be preprocessed, batched and processed - and thats before handing it to the driver for rendering....
Optimisation for DirectX Graphics (NVIDIA PDF)
Renderstate change costs
Basically any movement, light change, shadow change, shimmer, texture change or the likes will generate a state change causing the entire process to have to be reprepared from scratch - this increases cpu usage and inhibits gpu usage (it doesn't get enough data).
Batch Batch Batch! (Nvidia PDF)