It's good to know I can run them both. Maybe I'll grow to love V6 sometime in future, but now, I really like V4 better. BTW, I tried trial version of V5, but decided not to upgrade.

You should check out the 3D capabilities and the bezier masks available in V5 and V6. They can really open up some possiblities for you.

What exactly do you mean by 3d capabilities and bezier masks? Do you mean 3D transitions?

These are two features that were added in Vegas 5.

I am not talking about just transitions, Vegas now has 3D track Motion. You can tilt, zoom, rotate your video 3 dimensions.
For a sophisticated use of 3d done by one of the Sony Engineers, click here

Bezier masks allow you to create exact masks including curves.
For an unsophisticated use of bezier masks done by me go here. Then download the file, it's pretty big so you may want to save it rather than stream it. The audio is kinda loud too.

Here's how Sony describes these tools.

3D Track Motion
Create 3D motion effects with precise control over Z-depth, plane intersection, compositing and more. The Vegas 6 track grouping model allows multiple tracks to move and rotate in 3D space. 3D motion occurs in real-time and is instantly previewable via i.LINK connector*/IEEE-1394 hardware to external monitor.


Keyframeable Bézier masks
Produce keyframeable Bézier masks for complicated objects. Bézier curves let you closely track object outlines to mask and keyframe shape and motion changes over time. Create depth-of-field effects, apply color correction to specific areas of a clip, crop surrounding source material and create mask overlays. Multiple animated free-form shapes can be created in a single window, with mask invert control for each object. Feather and blend hard edges, set opacity levels for each layer, and zoom the workspace to the sub-pixel level for extremely accurate Bézier mask creation.

That looks pretty cool. I want to do some 3D stuff with titles, do they cover that in the Vegas manual?