The 7-4 makes the BeoVision 7 look lighter, whilst the 7-2 (or 7-1 in the case of the 32" BV7) can make the TV look 'heavy' and actually a little larger than it really is.
I'd recommend the 7-40 wall bracket if your wall can take it! Excellent piece of engineering and very very cool when it's working. You can mount the 7-4 to the wall bracket too, and the BV7 display will angle vertically independently to the 7-4 which is on a fixed plane. They both turn left/right with each other though, and fully motorised!
Sonically, when using other BeoLabs in the setup, especially BeoLab 3s, 9s or 5s, the 7-4 will give very noticeable sound improvements!