I have zero experience of either 5200s or 7200s unfortunately but I have had a couple of pairs of 5000s ove the years and a couple of pairs of 5500s which I had in a previous cinema room so I'm well acquainted with them although not for a few years & certainly not in this current room so any comments can probably be taken lightly.

From memory the 5500s hit a little bit harder and possibly went a little deeper into the bass but if anything the 640s are quicker & that initial crack of a gun-shot or a door-slam is terrific with them. I'm also finding that dialogue is extremely clear through my 3 640s & we've both noticed that we hardly ever ask "What did he say?" any more. And I'm a big fan of speakers behind the screen so I'm convinced you'll enjoy that aspect of it. My speakers are installed 'flat' ie no toe-in but I must admit that option didn't occur to me (or my intallers).

It sounds like you're giving the build a lot of thought so I'm sure you'll end up with a brilliant room.

Cinema: Meridian 271, 3 x DSP640 (behind screen), 4 x DSP320 (in-ceiling), 4 x DSP3100 (surrounds), 2 x AC12 (interface). 2 x Perlisten D12s subs, Lyngdorf MP40 processor. DT 145" 2.35 AT screen. Sony VW870 projector & S-T lens, Lumagen Radiance Pro.
Lounge: Roon, NUC, Kef LS50 Wireless + 2 x REL Gibraltar-2 subs

Meridian owner since 1998