If you build your own pc's , and don't mind being bound to Intel , you could always upgrade the memory , and see if you're happy . If not , you could use it in the new build .
You could also upgrade the cpu (and cooler) if you wish to a 9000 series to turbo up to 20% faster than the 8400 . (My 9700k turbos to 4.8 , as opposed to your 8400's 4)
You can then evaluate your 1070ti , and if you wish , purchase a more powerful 1440 p gpu , even at today's inflated prices , and with all the above upgrades still being within your budget .