The computer is decent as said earlier. Here are the main specs.
AMD FX-4100 CPU running @ 3.7 GHz
Corsair 8GB DDR3-1600 MHz RAM
XFX Radeon HD 7870 2GB
128GB SSD (668 MB remaining, and FTB is on the following hard drive.)
1TB HDD
Windows 7 Home Premium
While not impressive your computer should be running 60+ FPS, I have similar specs on my secondary rig and it runs 90+. What Java versions have you tried? I find I get the best FPS with Java 7 64bit and the most stable FPS with Java 8 64bit.