There is a tiny bit of a trouble with Tartiflette's SCY Nation mod, as their ships has dynamical maintenance, that depends on fleet state "stands still"/"on move", which leads to quite heavy performance issue.
But it's easy to overcome - if player has SCY-ships in fleet and took performance hit after adding this mod, said player need to drop said SCY-ships into storage, get on system screen, witness performance return and voila, SCY-ships can be taken back from storage.
I've found it on practice when after adding mod FPS dropped to ~25 on speeding time, from 60+, but as soon as I've done aforesaid it went better.