Jugiegal, yes, our vanity size and layout is very similar to yours. I really like your choice of mirrors, I am an arch person and like anything that has an arch element. But, because the two mirrors would have been this size, my kids really wanted a large one. When the girls do their hair, or each other's hair, or their friends' hair (you get the picture, right? :)), they stand in the middle and use the counter for all their hair accessories, hair dryer, flat iron etc. So it is important to have the mirror in the middle as well. The mock-up mirror in the photo serves this purpose now. And for me, it is great because it keeps all the hair-related products out of their bedrooms. Lyban, there is tile between the sinks but the upper row of the glass border is not there.

Thank you for your help! That's a good thought! Unfortunately, we've already primed the new drywall and have a single light electrical set up, so I think I'm stuck with a single mirror now based on the lighting. There also wouldn't be room for sconces on either side of the mirrors since the frames would be right next to the shower wall/bedroom wall if we had 2 so it wouldn't look as nice as yours!

The important distance to consider is the distance between the center of the vanity to the center of one sink. That distance never changes regardless of the size of the mirror. The wider the mirror, the less distance you have between the sconce and the mirror. If my calculation is right based on the measurements you gave, that distance is 21" (please confirm it as I don't explicitly see it on the measurements you gave us). The distance between the edge of the sconce and the edge of the 24" mirror is 6.25". This number came from that calculation: 21" -2.75" (half the width of the sconce) - 12 (half the width of a 24" wide mirror) = 6.25". Now if you use a 36" mirror, the distance between the edge of the sconce to the edge of the mirror would be .25" ( 21" - 2.75 - 18"). You don't want a quarter in. wall between the sconce and the mirror. If you were to find a 28" wide mirror, that distance would be 4.25" ( 21" - 2.75 - 14"). I think the width of the sconce is more in proportion with a 24" mirror. I also think a 24" mirror looks nicer with a 27.5 wide cabinet below it.

Without a picture of the space I am having a hard time visualizing this, but putting a 24" wide fixture over a 65" wide vanity sounds like the wrong scale. With that much room, why aren't you putting sconces on either side of a mirror? Lights on the sides of mirrors are much better than overhead lighting. A 40" wide mirror can certainly go over a 84" single sink vanity, but I wouldn't put a small overhead fixture over it. Do you have 9' ceilings? This isn't your style, but this is the closest picture I could find to what you're talking about. The side sconces fill in the empty space on either side of the mirror.