Personaly i am using java 7. I do not have issues. Ac
I have allocated 5GB. According to F3 i am using rangeing from 800MBto 2GB. And current ingame allocation is 2.5GB. It seems minecraft will allocate more if needed. So you can easly for start bump to 4GB.
Before uninstalling, launch FTB Launcher. Look at the top of console it should say something like this:
============================================================================
FTBLaunch starting up (version 1.4.3 Build: 10403)
Java version: 1.7.0_51
Java vendor: Oracle Corporation
Java home: C:\Program Files\Java\jre7
Java specification: Java Virtual Machine Specification version: 1.7 by Oracle Corporation
Java vm: Java HotSpot(TM) 64-Bit Server VM version: 24.51-b03 by Oracle Corporation
OS: Windows 8 6.2 (64-bit)
This will tell you which Java is default and minecraft is running. If it isn't correct, you can go to advance ftb setting and change java path
ill give it a shot. EDIT: this is what iit says directly from the console...
FTBLaunch starting up (version 1.4.4 Build: 10404)
OS: Windows 8.1 6.3 (64-bit)
Launcher Install Dir: C:\FTB
System memory: 4873M free, 7650M total
AnalyticsBackgroundThread started
The FTB Launcher has found the following Java versions installed:
Java Version: 1.6.0_45 sorted as: 1.6.0_45 64 Bit Java at : C:\Program Files\Java\jre6\bin\java.exe
Java Version: 1.7.0_71 sorted as: 1.7.0_71 64 Bit Java at : C:\Program Files\Java\jre7\bin\java.exe
Java Version: 1.6.0_45 sorted as: 1.6.0_45 64 Bit Java at : C:\Program Files\Java\jdk1.6.0_45\bin\java.exe
Java Version: 1.7.0_71 sorted as: 1.7.0_71 64 Bit Java at : C:\WINDOWS\system32\java.exe
Java Version: 1.7.0_71 sorted as: 1.7.0_71 64 Bit Java at : C:\Program Files\Java\jre7\bin\java.exe
Preferred: Java Version: 1.7.0_71 sorted as: 1.7.0_71 64 Bit Java at : C:\Program Files\Java\jre7\bin\java.exe
============================================================================
all in all i think it says that i am using java 7 (i added the ='s)