I have been sifting through a ton of forums and every single perfecto/ AKA Marineland 125 like this has been drilled in the back, and is only tempered on the bottom.
I am going to call marineland today and get a reassurance... and if it is drillable, I am gonna be one happy reefer.
I don't know how old your tank is, but on their site, iirc, none of the panes are tempered any longer on big tanks. But they have a chart on their site telling which tanks are tempered.