edit: i began writing this right after the excuse me posts so pardon if i mention BF which i see you dont like. it however does stress a good point :endofedit
The 250 Watt build should be able to handle all the latest games at the highest settings.
TinyVoices, please don't give out bad advice on these boards.
i do believe it is us who should be stating to not give out bad advice. the system just will not perform in the manner you wish. for example on bf4 max at 1080p
http://www.bit-tech.net/hardware/graphics/2013/11/27/battlefield-4-performance-analysis/3
with that said, its a reasonable attempt to make a small pc however it is not very cost efficient at all.
i tend to agree with the others here. it is a bit silly to try and limit yourself to 200-250w (just for the record your 250 tops out at about 285w full load) since we all know that actual power draw varies based on the task. the average mid-high level gaming system draws about 480w max load (i5-4670, 2 sticks ddr3, 1 hdd, 1 ssd, 5 fans, gtx 770) with upper end systems topping out at just a bit more. this is max load not average load. much more price effective as well.
that gpu you have is middle ranged at best. while it most certainly will handle some games at higher settings its an untruth to say it will handle them all. that would be like me saying my gtx470 can max out ALL games just because it maxes out all games that i play (which doesnt include bf4, bf3, crysis 3, etcetera. while it certainly can still max out many games its an untruth to say it can make out all.
i could see a possible need if perhaps electricity was very high priced (like in hawaii it is 33cents per kwh) or if you ran off a solar array however to do so you would be sacrificing performance. you will not get max settings on the most power efficient hardware however that doesnt mean its all bad. its not a terrible build for low to medium performance. if you threw in a better card you could kick it up however it would require more power.
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TLDR:
i think its an interesting concept but it doesnt quite work how you say it should. its also not cost efficient at all. while i do agree with some of your points there are concessions to make when it comes to making things affordable , making things good price/performance wise and when making something to play games on max.
i also think you shouldnt be saying the people are giving bad advice when in fact they were being completely truthful on the matter. you opened up the can of worms when you blanket statemented "all games" so he was entirely correct in his assessment and i agree 100%.