If a salesperson tells you that new windows will pay for themselves in energy savings, ask them to show you the math on your house. On most homes, glass is a smaller share of the envelope loss than the attic is, and a whole-house window replacement takes a very long time to recover on utility bills alone.
That does not mean the windows should stay. It means the honest reasons to replace them are different: units that will not open or lock, failed seals fogging between the panes, rot in the frames or the sill below, and single-pane glass in rooms that are genuinely uncomfortable in August. Those are quality-of-life and safety problems, and they are worth money on their own terms.
There is also a sequencing argument. If your attic is under-insulated and unsealed, insulation is a fraction of the cost of new windows and delivers more comfort per dollar in this climate. Do that first, then decide about the glass with better information about what is actually making the house hot.
When you do replace, the install matters more than the brand. A mid-tier window set plumb in a properly flashed opening with an insulated shim space will outperform a premium unit dropped into an opening that was never prepared. Nearly every leak and draft complaint we get called out to inspect traces back to the opening, not the window.
Ask for unit-by-unit measurements rather than a per-window average, ask what happens if rot is found in the framing once the old unit comes out, and ask who finishes the interior and exterior trim. Those three answers will tell you more about the outcome than any comparison of glass packages.