I would say the Pentas are the second closest to the BeoLab 9s, but the BeoLab 5s are much closer!
When BeoLab 5s are used as front speakers, at least BeoLab 3s should be used as rear speakers IMO, I just find that BeoLab 6000s or anything less don't really do it justice, especially BeoLab 4s which will really really struggle. Don't forget the BeoLab 5s are speakers which are capable of around 130 dB peak, possibly more. BeoLab 4s are only really suitable up to medium volumes in small rooms, and will not be ready for the kind of signals they would receive even as rear speakers when you're expecting them to keep up with 5s at the front.
The speaker settings seem not to affect the image as much as where the bass is sent, although with the BeoSystem 3 it does seem to make a difference to the image when using a BeoLab 7-1 instead of a 7-2. Maybe I'm just imagining things? 