Alright, I re-sampled the FPS drop and took a snapshot this time. I couldn’t find any function with “right” in its name in the results, but what I did find is that the Client Thread is receiving and processing a “S30PacketWindowItems” (presumably every tick), which ultimately winds up calling net.minecraftforge.oredict.ShapedOreRecipe.checkMatch which seems to be what is generating the client thread lag:
I thought BuildCraft might have what was sending the packets, but it looks like that thread was asleep for the entirety of the sampling period:
Edit: I looked up some of the function names in MCP. From top to bottom in the snapshot:
func_99999_d: run
func_71411_J: runGameLoop
func_71407_l: runTick
func_78765_e: updateController
func_74428_b: processReceivedPackets
func_148833_a: processPacket
func_147241_a: handleWindowItems
func_75131_a: putStacksInSlots
func_75215_d: putStack
func_70299_a: setInventorySlotContents
func_75130_a: onCraftMatrixChanged
func_82787_a: findMatchingRecipe
func_77569_a: matches