When Nuclearcraft is installed with GT4, NEI’s recipe lookup performance is greatly impaired.
Freezing happens whenever an item's recipe is checked, even when such item has no recipe:

The freeze is directly proportionate to the number of items in-game.

Logs with B:Debug and B:Debug2 enabled:

FML Latest log:
https://pastebin.com/kqyx38VN

GT_Oredict log:
https://pastebin.com/1zwd6csV

While GT4 reports errors with the oredict names from Nuclearcraft, the issue remains even after names are made compatible:
https://pastebin.com/TujfN59C

Stripping all NC classes related to the Crusher/Electric Crusher content and its NEI API fixed the issue