I started a separate post about this as I didn't initially find it under searched here. It did come up on Google though.
It seems apt-get install xfce4
Does improve performance but it's still not as solid as Kali 1.X was ...
I'm running Quad 2.X with 4 Gigs of Ram - My computer is not 4 years old and while it isn't i5 or better qith a quad processor it should be able to handle the load. It also has a 1GB graphics card. Not a premium computer but should be more than sufficient for any Linux Distro.
Maybe this should be moved to bugs section and looked into ?