When I am close to a steam system that is building up to speed. As in a collection of steam turbines that are not being fully supplied with all the steam that they can consume FPS takes a massive hit going from 60FPS to 15FPS. Once enough steam is being generated to fully supply all turbines the FPS hit disappears seeming to be related to steam turbines when they are not being fully supplied with steam.

When turbines have no steam supply though FPS is fine. The problem occurs when there is a steam supply that does not fully supply a turbine such as when a large boiler is warming up

Also the FPS hit decreases as you get further away from the turbines even when they are in chunks that stay loaded

Is there a tank in-between your steam production and the turbines? I had this issue with Simple Fluid Tanks multiblock, though I guess it could happen with others as well. If steam is being taken out faster than it is supplied, the way the block looks like will keep changing every tick (changing between empty and not empty), causing a lot of chunk re-draws. If that's the case, setting Mod Settings -> Minecraft Forge -> Config -> Client -> Force threaded chunk rendering to true might help, or better yet building some simple redstone circuit that will disable extraction for a moment if the tank is empty.

Yes that fixed the problem. I had an EnderIO tank for storing some extra steam. Thanks the fix worked perfectly

Glad I could help! If it turns out that your issue wasn't actually a problem with the modpack it's best to close it here.