I think the Beta will be pretty feature-complete with no major changes coming to the RC, unless there's a large amount of criticism because of some of the new UI choices/gimmicks compared to earlier versions of Windows. I think Microsoft wants this out of the door fast and my schedule has a smaller gap between RC and RTM,:

Beta ??? Feb 20
RC ??? June 2
RTM ??? July 16
GA ??? August 27 (Heavy back-to-school marketing?)

Too sunny?