dtgreene: 2. In terms of discrete GPUs, which ones are best if I am concerned about energy efficiency? (Most recommendations seem to be based around raw performance, but high power graphics tend to use a lot of electricity; what if electricity use is the main concern here?)
This is not a direct answer to your question, just a general remark. Part or all of it may be bullshit, but who cares.
I think with mobile discrete GPUs the laptop vendors are more concerned about the heat generation of the GPU, rather than how much power it uses. Of course these are partly related: in order to fight the heat, either you use lower power GPUs, or make the ventilation of the laptop better (which in itself may use more power too as better when you start adding several fans that spin faster; e.g. my gaming laptop has two fans, one near the GPU and the other near the CPU).
That is why most laptops have another GPU as well, a lower power Intel HD or such. So the general idea seems to be that if you are going to run so demanding applications/games that the discrete GPU is needed, you should be plugged in anyway, not on battery power. If you are on battery power, the assumption is you will be running less demanding software (e.g. office applications etc.) for which the integrated low-power GPU is enough (e.g. Intel HD).
As for your actual question, generally speaking the newer the mobile GPU is, the more power efficient it seems to be. This doesn't necessarily mean it uses less power, it can also mean it is faster using the same amount of power as its predecessor.
This may exclude the very top-end mobile GPUs of each generation; for them the idea quite often seems to have been to be as fast as possible, even if that makes them more power hungry. With a few steps lower on the line, with GPUs that are new revisions of older models, the idea seems to have been to improve their power efficiency (rather than their raw performance), maybe so that they can be installed on smaller laptops too and not just the biggest 15.6" and 17.3" laptops with better ventilation.
I am unsure how power efficient the latest NVidia Geforce 1xxx GPUs are, the ones which don't have the "M" at the end of the name signifying they are specifically mobile GPUs. The little I've read about them, at least the top models do require very good ventilation on the laptop, implying they use quite a lot of power (hence the heat generation). On the flipside, they are also quite powerful, offering pretty much desktop-level GPU power.
https://www.notebookcheck.net/ may offer the data for you, at least they usually point out how much power each GPU uses. Not sure if they let one to sort all the mobile GPUs by their power usage, and then try to pick ones which seem to offer high raw power for relatively low power usage.
Not sure if Notebookcheck has an user forum, maybe it would be a good place to ask?
EDIT: It also occurred to me that crypto currency miners have probably some idea of this, as they are so concerned about getting as much GPU power for certain amount of electricity, in order to break even (and then some). But I guess they mostly use desktop-level GPUs, not mobile GPUs specifically. Not sure if there are some crypto-currency forums where users are discussing about this, which GPUs give the best performance for their electricity bill?
Is that why you are asking, starting a bitcoin mining farm? :)
