I just looked at your scene, jeez dude, talk about complicate your scene. first use a spot light for the over head light with a nice penumbra for the falloff, this will make life a little easier other than that get rid of the other light start simple when it comes to lighting and add as you feel needded. I then noticed youve pasted the material from one glass to the next, just create a new mia x material and drag and drop onto the glasses, theres no need to copy and paste them, this could be half the problem too as mental ray can get a bit odd at times.

also having that black backdrop will certainly not help matters overall, but by using the one shader will cut down on your settings. Also switch on and off the raytraced shads on the light to get an idea of what settings in the render panel to crank up or down. I reshot your scene in 2 mins and it was fine for a test shot, just a few tweaks here and there to help it but other than that this made all the diffrence to the output.

Jay