If you didn't create anything, IC CAN't cause FPS drops. Period.
However, probably MCforge overwrote some parts of Optimine or whatever and thus removed the FPS boost?
Optifine and Forge work beautifully together if Forge is installed before Optifine.
Even on flat world 25 fps..wtf
I even closed PS,Skype,ICQ,Chrome,AV and defrag 
I had this happen yesterday. I couldn't figure out wth was going on either. It just randomly happened after closing MC for about an hour, came back and suddenly all that was happening. I even tried on a flatworld too and I was getting like 22-25 fps. I closed EVERYTHING as well, I even defragged both partitions of my hard drive, ran some diagnostics, scanned for viruses and stuff. The only solution to the problem was...restarting my PC. I have no idea wth that had to do with MC, but it worked. (Note: Tested other games, everything else worked perfectly fine.)
Tried that out as well
I noticed,that changing texturepack to LB photo realism ( my default pack ) gave me like 10-15 FPS,however I had ~30 with it on 1.0.0
It sure is problem with modloader/forge/optifine,which dig up all the game mechanics,it's impossible to external mod,like IC2 to cause such things
Also,something new.I'm having constant ~1,5 cm red lag and ~7cm white lag,never seen that before..still,this shouldn't be posted ion IC2 forum..gotta think something about it.. 
It sure is problem with modloader/forge/optifine,which dig up all the game mechanics,it's impossible to external mod,like IC2 to cause such things
YesNo.
Per se, installing IC cannot cause such things.
However, if you build a giant 32x32x32 cube of cables or similar constructs causing massive calculations, it may can.
