I rendered the same scene using mental-ray and v-ray:
for each scene I applied different materials and lights, using the standard shaders (VRayMtl and mia_material_x) keeping the default options and changing just the necessary to render refraction, caustic and shadows.
My computer is a Dell Studio Xps 13, Intel Core 2 Duo P8600 (2,40 Ghz, 1.066 MHz, 3 MB), SDRAM DDR3, 4MB, with Windows Seven.
Render time: 5:22 sec
Render time: 1:12 sec
I prefer the V-Ray render, the quality of the refractions and caustics is much better, but the render time increases a lot!
Feel free to change attributes and try new renders. If you download it, feedback is welcome, thanks! 🙂