I made a thread telling people how to improve their FPS found here Info - Tips on how to Increase your FPS | MineYourMind Community But after some testing and looking around i found something interesting, Journey map causing lag There have been many reports about it, here is one 1.0.1: Massive framerate dropping and load stuttering | Feed the Beast Also on the FTB site many know user will tell you to remove this map mod. In my opinion Zans combine with opis is "better". you get a mapwritter like map with the mobs on your mini map from zans.
it may not effect you but it effects enough people that it is recognized as causing lag. edit: i noticed you said "much". a mini map should cause no performance issues
opis can be heavy on clients, especially when the overlay is enabled. In 1.6.4 there is also a memory leak, not sure if that exists in 1.7, too.
