Should I buy the B&W 804d's or 805d's

Get the 804Ds They are better balanced than the 803DIs. I had 805Ns with a sub and could never get the bass to sound correct. I think you will have better bass integration with 804Ds. Besides the 804Ds & 803DIs have a way better mid-range. I was quite shocked of how 804Ds and 802DIs were very similar compared to 803DIs. Tonally speaking. The 802DIs were better than the 804Ds but 15K is a lot of money

Ok the room will make a big difference. My experience is monitors with a sub should work out better. That being said my room is 12' X 26' with the speakers on the long wall (I have no other choice). I used to really like B&W until I heard the Dynaudio's. I own the C1's with a Rel B3 sub and wanted to upgrade to the C2's. So my dealer loaned me his C2's for a week. What I found the C2's was a wall of sound. Not bad but I really prefer the monitors in my setup. Now at the dealer he has a much bigger room and the C2's just blow away the C1's.

Just my experience with my room

Has anyone actually heard the 804d and 805d to compare?

When I liked B&W I compared the 805d to the 804d 803d and 802d's. Thats why I first recommended 803d's. When I did demo them they in at the dealer in a 20' 30' room. Also when I listened to the 805's they did not have a sub connected. So my personal opinion the 805s with a sub would be what I would recommend based on my experiences in your room.

Ideally you should demo them in your room with your electronics if at all possible. Everyone has their own opinion of whats sounds best.

Xti16, how would you compare the 805Diamond's to the C1's in overall terms.