Well MR is crawling in the following situation: If I add grass (fur) to the plane, MS will render it fast, but MR will crawl due to it.
I don't know why MR is crawling like that, I don't know how the scene is setup. As for area lights their scale affects their intensity and shadow softness. If you're using MR then you can use the light shape option in the light shape's 'mental ray' section.
Try a different texture with more noticeable shapes on the ground and check out the maya software, it probably will make it look messy as well.
To be honest I can't remember the last time I used the software renderer so I have no clue why the texture is such a mess in the reflection, however I believe the reason why the fur wasn't showing in the MR render reflection is because 'visible in reflections' was unchecked in the render stats section of its shape attributes.
This render took 1min 1sec using 'production' render preset on a quad core 2.66GHz machine with 8GB DDR2 1066 Ram.