i7 costs more because it has a video chip in the processor but they ain't very good for video games
if the unit has a video card esp with 6 G they are better then the chip and no need to get an i7
and a fast i5 will save a 100 or so
except for the top of the line i7 you can get an i5 that is as fast or near enough but speeds on both vary a lot
they check and up price the better ones and the slower ones are cheaper called binning
newest faster thing is a m2 card on the PCle instead of an ssd on a sata3 conection for the HD
the m2 unit is almost 10 times faster then the ssd that is 10 times faster then a old HD
well worth 50 to 100 bucks over an ssd
https://www.makeuseof.com/tag/pcie-vs-sata-type-ssd-best/
most computers can use more memory but some older ones can't go to big like apples
check the exact model year ect