The original 4Gb tweaker of this thread (in fact an internal flag in any Portable Executable, in any .exe) specifies if when executed memory blocks over 2Gb can be addressed or not by the operatin system. It only is an adnvantage for some applications. It was not determined schientifically if it produces a benefit or not (some people say yes, others can't recognize any difference).
The other JSGME MODdable executable versions are just different il2fb.exe with the -Xmx (heap memory of the java Virtual Machine the game uses) set to 512/1024, etc.
Since previous version made by Kegetys, later SAS~Storebror developed the recent versions of the il2 selector which includes a pratical way of setting not only that, but even other of the Java Virtual Machine starting settings. After him my TotalMODder offers similar chances of adjusting in detail any memory parameter, including a simple slidebar (as Storebror did) to set the Heap Size.
The last explanation referred to Java yes have clear and empirically testable results. It expands the number of classes (planes and other objects) you can use, and practically supress the micro-stutters thagt otherwise used to shortly hang the game when playing.
But there is no fixed rule regarding the heap adjustment, and it produces different results in different systems. So trial and error must be applied to achieve your own optimal settings.
Regards,
Pablo