Wing-It's are designed for grab bars. I'm not certain if they have a 3-screw adapter that you could screw into the Wing-It that would allow you to hang a mirror from it instead of it being a grab bar anchor.

For large and heavy mirrors, I usually craft a french cleat from scrap wood and integrate it as part of the mirror's frame. I make my own frames, btw.

A derivative that you could purchase would be something like this, it's called a "Hangman":

Mongo

I agree with mongo, I wouldn't use a hollow wall anchor for a really large heavy mirror. I used something like he has pictured for a large mirror behind my wet bar that probably weighs in excess of 80 pounds. The one I used was called a "z bar".

Thanks, great information. I will definitely make use of it.

Meanwhile I have another mirror that pivots on brackets mounted on the sides of the mirror. The brackets are what need to be attached to the wall. I wish I had had my builder reinforce the wall behind the sheetrock in this spot.

I've used SnapToggle toggle bolts to install all kinds of things on my difficult to hang on walls. My 80 year old house has 1/2 inch sheet rock over plaster and lathe walls. Many conventional anchors don't work well because of the thickness. My most recent application was hanging a 52 inch LCD TV on the wall. I love these anchors, they will work on any wall and are very strong.

Here is a link that might be useful: SnapToggles