Also, sustainability of a web server doesn't mean that much if you don't consider the net impact in the world. It seems to me that you could have a web server require substantially more power and still be a net benefit if it actually influences many users to consume less in their daily lives.
What is the marginal cost of the web traffic it creates and replaces? Would tuning the software and data payloads be more impactful than worrying about the server wattage?
What is the marginal cost of other user activities which it influences? Not just the website operator, but the user behaviors happening as a result of their relationship with the service? Do they stop using other less efficient services or just increase their overall footprint? Could it reduce their consumption of energy and material goods? Change their diet or travel habits...?
What is the marginal cost of the web traffic it creates and replaces? Would tuning the software and data payloads be more impactful than worrying about the server wattage?
What is the marginal cost of other user activities which it influences? Not just the website operator, but the user behaviors happening as a result of their relationship with the service? Do they stop using other less efficient services or just increase their overall footprint? Could it reduce their consumption of energy and material goods? Change their diet or travel habits...?