that a wet dream of a build and your asking what needs upgrading?
solid gold case?
double glazed windows os?
take your mrs out, your pc's *** hot
if you dont have a mrs rent one with the dough youve just saved
I'd move away from stock cooling especially with a system like that, i'd probably grab something like a Corsair H100i and do some overclocking.
And considering you said you do not want to upgrade your CPU or GPU then i see nothing else really. You could always get another SSD and put them in RAID 0 for some extra speed. But overall it's more then a decent system.