Those settings are pretty much what our installers generate:
D:\dev\test-installs\ME5GA\eclipse\eclipse.exe -product com.genuitec.myeclipse.product.ide -vmargs -Duser.language=en -Xms128M -Xmx512M -XX:PermSize=64M -XX:MaxPermSize=128M -Dosgi.splashLocation="D:\dev\test-installs\ME5GA\ME\eclipse\MyEclipseSplash.bmp"
MyEclipse 5.1 will monitor heap space (all flavors) and alert you when you’re within 5% of the maximum. Another way to check up on it is to show the heap status in the status bar at the bottom with Window > Preferences > General > Show Heap Status