you are comparing apples to oranges...
the one you linked is $1458 while the one i linked is $1145. this isnt a fair comparison so... with that much of a budget increase i could throw in a 780ti to the one i linked. its then more of a fair comparison with the prices being about the same.
the 290x and 780ti compete side by side with neither having a big advantage. see here
http://www.anandtech.com/bench/product/1056?vs=1072 it seems that the 290x you listed is a decent price though. i prefer nvidia cards since i like the software and they support phyx but amd cards are good IF you can get them at a decent price (the bitcoin mining market drove prices up for awhile)
the i5-4670k however, steps all over the 8320. you can overclock the 8320 into the performance realm of an i5 however its really not the same and you can overclock the i5 to blow it away. for builds less than $800 amd makes alot of sense but for greater intel does. intel wins on performance, power consumption and thermal output but not on price. keep in mind that the amd fx chips run HOT and cant take a whole lot of thermal abuse so you need a good cooler and if you overclock this is doubly true. intel chips are easier to manage so you dont need to worry as much (but a good cooler is still good to have).
keep in mind that the build i listed also included a ssd. while its not large enough for lots of things it could handle the OS and a few programs for snappy windows performance and quick booting (as little as 9 seconds sometimes). of course it doesnt help for games so can be removed if you want pure gaming performance and dont care about startup times.
the build they listed had a bigger power supply. unless you plan on adding a second gpu this is not necessary. if you went with a 780ti on a build like mine i would likely say get a 600 or 650w for a bit more headroom but it might be okay on a 550 (i'd have to run the numbers to check).
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if i bumped the gpu up to match the build you specified... are there massive differences?
yes and no.
graphics wise... they would be fairly even.
the intel chip is more powerful so wouldnt get bogged down like the 8320 might in certain scenarios like multiplayer gaming.
the intel system would likely run cooler and draw less power from the wall.
with a ssd the boot time would be about 9 sec (ssd) to about 30-60sec (hdd) between the systems. this doesnt improve game performance though. windows will also feel faster on the ssd but slow (like computers from 2008 slow) since hdd technology hasnt advanced as far as speed very much. (ssd is what was developed because hdd are at their performance limits)
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i would have went over all these differences if you had wanted to take me up on my offer before