I think the automatic downshift from 6th to 5th is a good thing. I use that feature (in lower gears too) when I want a quick downshift for more power.
I haven't tried to floor it in 6th. I've done it in 2nd, and it stays in second.
I also think it's a good thing that it shifts up automatically. I know I wouldn't want to accidentally exceed the redline. Maybe if this were the SVT and I was on a road course, it would be a different story. But for a family car on the street, I like the way the transmission works.