I just started playing Mindcrack but I was having a lot of fun nearing end-game with Direwolf20 V4. I hope I don't have issues like that, though sometimes I notice some lag spikes when I was just building my first base.
Anyway, I'm wondering if you could try something that has helped me. I was having some severe FPS drops in my Direwolf20 world and I accidentally stumbled onto a fix that has helped me even smooth out Mindcrack.
While the game is running open up task manager. You should see two Javaw.exe running. One is for minecraft and the other is for the console. Just disabling the console via the launcher will not close the second Javaw.exe. I manually end that second Javaw.exe process, it is the one using less memory. For my computer it makes things smoother. If you try this please
back up your saves just in case, though I never had a problem but I don't want to be the cause of someone losing all their work.