Minecraft is mostly cpu intensive with not much demand placed on the gpu. An i5 should do just fine, many with i5's and even a moderate gpu with 8-16gb of ram are in the 100's of fps even modded.
Maybe not a decisive benchmark but some other users experiences based on their setups.
https://www.reddit.com/r/feedthebeast/comments/2d6vbo/those_of_you_who_get_over_60_fps_in_modded/
I'd stick with the i5 personally and overclock it. Unless you're using something like optifine I believe it is, minecraft generally doesn't make much use of hyperthreading. Faster cores make more of an impact.