^^ Oh no no no.. That "more than 4GB" remark was for the "system as a whole"
I know that beyond a point, RAM allocation has a detrimental effect on Java performance. (I've stared at that @
Eyamaz thread on JVM arguments for too long
)
When you allocate 3 out of 4 GB just for minecraft, the OS performance suffers (YMMV), and if you opened a chat application plus a browser window for wikis and videos, it gets more squeezed for space. So, if OP wants to get more RAM, then investing in it might not be a bad idea after all.