The Low E coatings are amazing. We were doing an addition of a room that jutted out like a peninsula and had large windows all the way around. It was mid August in Southwest Florida and so hot that we'd have to quit shortly after noon to avoid heat stroke. The roof framing and sheeting was brutal.
We dreaded working in the room after we installed the windows because we were just sure that it would be like working in a solar oven. The windows were lowE coated and blocked all the heat, even in full sunlight. That's when I became a believer.
The windows (and sliders) I'm talking about were coated by the manufacturer. I don't know if you can have them coated aftermarket, but if you can it would be a good alternative.