GPU Only or CPU+GPU

Hello. I have Intel i5 4590S CPU 3,70 Ghz and GTX 550TI Gpu. Usually, i render cpu only, but now, if i do CPU+GPU, or GPU only, which one will be faster?
I render in 1280x720 resolution, 2 characters, bed, background pic. It takes 1-1.5 hours to render this. Which option will be faster for me?
Comments
You'd have a hard time fitting even that scene into 1Gb, all the VRAM the 550ti has. Even if you do it probably won't make a lot of difference. the 550ti has nearlt no CUDA and that is what increases rendering speed when doing gpu renders in iray.