I have a good customer who is looking to r/r ~twenty single pane (Likit brand)aluminum windows with modern dual pane aluminum windows. The homeowners have a strong preference for plain dark anodized aluminum frames over (aluminum clad) wood, fiberglass, or vinyl frames.   I have been getting information from a multitude of good sources and welcome any suggestions.

While the budget is not unlimited, cost is not the first,second or third concern to these homeowners. What they are (hoping) for:
Highest quality sealing/movement hardware
Thermal break between inner/outer frames
Modern glass package (double pane, low E, tinting, tempered/laminated…)
Ability to obtain replacement hardware years down the line.

The two most common window styles in the house:
A floor to ceiling single hung window where the bottom third opens
A ~6′ wide x 3′ high horizontal slider.

Thanks again to everyone,
Dave
p.s. There are also several sliding glass doors they would like to update as well.