I would strike number 5. In many ways, the syntax differences between .NET and VB6 is an advantage for .NET. OO design was developed partially to enhance reuse. This is accomplished in my opinion. You will be able to do more things faster once you get going with it.

I feel that the only valid point is the fact that you are supporting older legacy systems. Otherwise, .NET is superior. I'm not sure that I would care to deal with it on older systems, though.