AD topic - Minecraft is significantly faster when run under 64bit Java, with large enough memory available. Too bad Dwarf Frotress cannot, and will not be able to take advantage of 64bit systems.

Honestly I personally don't really care if a game is 64 bit or 32 bit. I see a 32 bit as a good way for me to multitask. At least I know that the remaining ram can be used to run other programs instead gobling up all of remaining ram, whatever I am not using. I think these days it is all about the graphics card, Since graphics cards has like a max of 2 gb unless you go insane on your graphics card with 7gb of ram, 4gb is pretty sufficient, remember graphics cards pump out numbers and ram does logic.

64 bit apps do use more memory but they don't magically use all of it.  They use as much as the game needs, just like 32 bit apps.

How much would it theoretically cost to make a 64-bit Iron engine?