Fps Increment is always hard, It's a bit of a struggle for certain systems.
as Kuzey said, RAM is always needed to be allocated to the game especially for a modded game, you should be able to do this in the settings of the launcher.
Put your minecraft settings to these with optifine:
Some of those settings may not be there, ignore that.
Try going into task manager (LSHIFT + LCTRL + ESC)
Go into the Processes Tab, Right Click "Javaw.exe" and go into the priority drop out menu and click "high", this will put your minecraft client as its main focus of performance should top up fps by a bit.
When Allocating RAM try to Allocate roughly about a half and a bit of what you have, so if you have 4GB of Ram, allocate 2.25gb of ram, Allocating too much ram will drop your fps rather than raising it.
Try not to use texture packs aswell.
Hope this helped.