Originally Posted by GoodDayToDie
Power consumption curve for CPUs is very non-linear. 90% from 100% will probably save you more power than 20% from 90% will. You'd just be wasting a ton of processing capability.
Not only that but the windows throttle percentage is not really as specific as a 0-100 range would suggest, so even if you set 20% it might limit the cpu to its minimum frequency.
If you use a tool such as this you can see what the current frequency is: http://www.cpuid.com/softwares/tmonitor.html
With my laptops (much slower) Core2Duo the minimum frequency was too slow, but about 50% of the max worked well and dramatically reduced the heat under load.
Some people reckon it is better to allow the cpu to use its full frequency so that it finishes the job faster and can move back to the lowest idle state. I am not sure that really applies to i5 (which doesn't support the ARM-style idle states that haswell will) and like you say the power consumption at lower cpu frequencies doesn't vary much. My experience with windows is that sometimes for no apparent reason at all programs such as word or chrome sit using 50+% of the cpu and you have to restart the process. It doesn't happen often at all but you might not realise until your battery is low. With the pro's i5 I expect you could get away with quite a low cpu frequency and would at least know you will always get roughly the same battery life.