Rendering Time

This is definitely not very fast. Looks like the higher the tile the faster it is. CPU works and renders the picture faster but takes longer to finalize the full render. But, this is all alien to me so what do I know!

GPU Nvidia GeForce GTX780M
Processor 3.5 GHz Intel Core i7
Memory 32 GB 1600 MHz DDRs
Mac-OS X El Capitan
Blender 2.77a Mac 64 bit

Time: 2:38 (GPU CUDA) 512 Tile
Time: 0:04 (GPU) 512 Tile (Grainy)

Time: 2:49 (GPU CUDA) 1028 Tile
Time: 3:41 (CPU CUDA) 1028 Tile (Grainy)

Time: 6:45 (GPU CUDA) 64 Tile