Buy VisualMill 4.0 now and pay $500 later....

Dear Fellow members:
I'm wondering if I should get VisualMill 4.0 now and then get the
upgrade to 5.0 for $500? This would be less expensive, at least
from what I can tell from Bob Campbell's website, than waiting for
the full VisualMill 5.0.
I'd like to get VisualMill since it seems like a professionals'
product and I don't want to jump from software package to software
package later. My CAD program is TurboCad Professional version 9
and I'm planning on using Mach2 to drive the steppers.
I was thinking about MasterCam Mill v. 9, full axis, but this is
too expensive and not really what I need.
So, would you get 4.0 now and 5.0 later and save $1500 or is this
not possible anymore? Thanks in advance. Later, Jim