Alright, I got in finally and gave that snapshot (GregTech 6.14.11-42-gcd777392 according to the Mod Info screen) a test . Unfortunately, it looks like the problem is still occurring. I tested with a Thorium Wire Cutter and a Thorium Axe.
Holding right-click when using either of those tools when aiming at nothing but air causes the FPS to drop.
Using the Thorium Axe on most blocks also causes the FPS to drop.
Using the Thorium Wire Cutter on most blocks, however, causes the tool to be swung and does not produce an FPS drop.