After upgrading our hosts to rhevh-6.4-20130318.1.el6_4 and our guests to EL6.4, I have noticed some significant performance improvements in the SPICE protocol.

In particular, the performance has seemed to improved in two cases:

- Large display resolutions -  For example, the monitor attached to my office PC is 1920x1200.

- Some commercial EDA applications -  I'm not sure about which features of these applications benefited from optimization.  The Help application is orders of magnitude faster.