Cycles Render times

My times have not been that good. GPU was the worst. I’ve tried a few different things, but CPU 8x8 is the best for me.

My time:
CPU: Intel i7-3720-QM 2.6Ghz
GPU: Nvidia NVS 5200M
OS: Windows 7 64bit

8x8 ==> Time: 7 min 8 sec
8x8 (High Priority): Time: 6 min 32 secs
16x16 ==> Time: 7 min…
120x135 ==> Time: 7 min 9 secs
480x270 ==? Time: 10 min 51 secs

480x270 ==> Time: 26 min 54 secs
512x512 ==> Too long I had to kill it.