Well seeing as I've installed over 1000 backsplashes with 1 ¼ screws(I just measured it), that never make it through the back of a plastic box, I'd say I might know what I'm doing. I would imagine a 2 inch screw would be a bad idea. I do not carry that size.
I have used 6-32 extended bolts for a while, until someone had already used drywall screws in a box on the whole entire backsplash, ruined threads... And now a 45 min trip to Lowe's to get drywall screws, and in a world where you need to make money and not waste time, in-comes 1 ¼ screws.