For now, definitely run 3.8 with 8GB. You'll never use 16GB with current games.
^^^^^^
That's the correct answer. Virtually all games will actually run fine on a 64 bit system with 4GB of RAM provided you aren't running Vuze or 30 tabs on a web browser at the same time.
I'm saying that as I write this on my gaming PC - a Q9550 / GTX 260 with 4GB of RAM on Win 7 64 bit. I have yet to find a game that causes RAM issues with my gaming PC at 4GB (games include Civ V, WoW, Homefront, Planetfall 2), though I would recommend 8GB. 16GB is a waste of money for 99% of users.
My iMac has 12GB. With 12GB, I can run my iMac in native OS X with VM sessions of Win 7 with Visual Studio 2008, Solaris x64, and Windows Server 2008 with SQL Server 2008 at the same time - and I don't have memory issues. The reason I do all of that is to simulate a production environment for development, so if you don't have such a need you probably don't need that much RAM.