"SolarGard and 3M claim Low E help during the winter." - of course they do; they sell windows. But which one do you want for your climate?
Windows with high solar-gain low-E glass are designed to reduce heat loss while admitting maximum solar heat gain. They are best used in heating-dominated climates, especially for passive-solar design projects. They usually incorporate an argon gas-fill, and the glass is typically made with a pyrolytic low-E coating.
Windows with medium solar-gain low-E glass are often referred to as spectrally selective, and they reduce heat loss while allowing a moderate amount of solar heat gain. They typically use an argon gas-fill. They are usually made with sputtered low-E coatings.
Low solar-gain low-E glass is also spectrally selective and is best suited to cooling-dominated climates, where the biggest concern for windows is blocking heat transmission. These windows are made with sputtered low-E coatings that consist of either two or three layers of silver. They are sometimes called double-silver or triple-silver low-E windows.
Also, I took the liberty of fixing their plug:
'Low emissivity prevents heat from escaping through windows while keeping out 52% of the sun’s energy.'
"Low emissivity prevents heat from escaping through windows
in the Winter. Spectral selectivity lets in 68% of natural light while keeping out 52% of the sun’s energy."
So I can't really answer the question, other than what logic dictates the "biggest concern for windows" is.
52% loss on solar gain vs 'emissivity'. Whatever that computes to.
According to some utility company, yes. And it's climate dependent for which side and which piece of glass should be coated.
A double-pane window with a low-E coating will have an R- value equivalent to or better than a triple-pane window. Windows in warm climates, where cooling is the primary concern, should have the low-E coating on surface 2 as shown in the figure below. In cold climates the coating should be on surface 3.