I set it to 2048 and 1024 (2GB) and immediately saw a difference. The game didn't have any skips in framerate when loading the map, which it used to always do. I think it will just smooth out the chunk loading and make it have less of an effect on your framerate. I'm not sure about loading new chunks though.
Stop wasting time on pointless tweaks to such a simple game. You will only bug it.
For users with 64 bits machines with 64 bit JVM the game eventually enters the 64 bit address, and by eventually I mean it will seldom enter the 4Gb memory range.
For users that, on top of 64 bit architecture, use visual range modders, then it might be a good idea to allocate more memory to the game, though JVM and the OS will do that automatically, so no need to tweaks like these.
I am on a 32 bit os and have 4Gs of ram and whenever I type in javaw -Xmx3072m -Xms1536m -jar "C:\Users\Chase\Desktop\run minecraft\minecraft.exe" It says "Could not create the java virtual machine." as well as. "A fatal Exception has occurred. Program will now exit." Please help me with this, I have over 40 mods and I want to run minecraft with 3Gs of ram so it won't lag as much. Thanks.