Dont go for the APU build
-fx 6300 way over 7850k cpu
-r7 260x way over 7850k's gpu even if dual graphics is enabled
Now about the first build some fixes
-the 600w is more than you need really. You could buy same model from evga but on 500w
-the 260x is good gpu but it will perform the same in a fx6300 and athlon x4 750 if you get my point.
http://www.tomshardware.com/reviews/build-your-own-budget-amd-pc,3807-2.html
-if you can buy a r9 270/x for 40-70£ more , than you have reason enoughs to stay with the fx6300.
-the 500w PSU wil suffice both cases.
The 270x is a real win really its for 1080p on high/ultra. 260x is fo 720ultra and 1080 med/high.