Noticeably better but you will need to change your motherboard so it is not worth it as you can get a very near performance with a i7 for your motherboard, like the 6700k or 7700k (if your motherboard allows overclocking, you can probably outperform the 8400). I have a 6700k at stock speeds because my MotherBoard has the B150 chipset and doesn't allow me to overclock, and it's a perfect match for my 1070 (in the most stressful scenarios in Battlefield 1 the CPU can reach the 100% usage but the GPU usage is still 98-100% so the bottleneck is almost zero).