Im wondering if the problem is with the world... or the modpack.
What FPS do you get if you start a brand new world? Is it still 5-10fps?
I have a very beefy system, but I have had problems with optifine Causing lag rather than fixing it. Eventually i found the 'D1' version which fixed a lot of things.
I also saw you installed java 8 instead of java 7. I dont know how well FTB is tested with java 8. Most folks run java7.
So.... try this:
1) uninstall java -- EVERY SINGLE VERSION.
2) Attempt to run FTB -- you should get an error about java not found. If it runs, stop and report back here
3) Install java 7 64bit
4) Attempt to run FTB -- The launcher should start. check the console log in the launcher to make sure it found only ONE version of java
5) goto options, set RAM to 2GB. remove any extra JVM arguments
6) edit your FTB modpack and (temporarily) disable theses mods:
hats, hatrack, opis, waila, zan's minimap, mapwriter, journey map, Reis minimap and Optifine
(dont worry if some of these are missing)
7) start a new single player world.
How is performance?