What size mirror for my vanity?

My hall bathroom is 8 feet deep and about 7 feet wide so when you walk in the door, the vanity is to the left and shower and toilet to the right. I am replacing the 8 foot long wall to wall vanity with a 6 foot, double sink vanity along with a 2 foot wide pantry (on the far end). That new vanity will go wall to wall again and we want a full width lighted mirror above it, with two light fixtures above the mirror, centered over the sinks. Once the counter and backsplash are in place, there will be 48" of wall from the top of the backsplash to the ceiling. If all that paints a picture, here is what I am thinking:

Either a 60" or 66" wide mirror because 72" will go wall to wall and I think it needs a little exposed wall on the sides. 60" would line up with the ends of the sinks, so I am leaning toward that. The bigger question is 30" or 36" high. There will be some outlets between the mirror and the backsplash, likely horizontally orientated, so the mirror will have to be a little higher to allow for that, then there will need to be room at the top for the fixtures. I am thinking 60 x 30 but wanted to run it by you guys and see how much space should be at the top of the mirror. Thanks.