Update your settings

Dear all,
Context:
We use Profinet communication.
I have 1
S7-1500
as data concentrator to populate a Rack-PC supervisor
WinCC
.(connected with PN)
The
S7-1500
retrieves
20 DWords
from all the
30 S7-1200
on the field to update
WinCC
.
The
S7-1500
also sends
2 DWords
to all the
30 S7-1200
on the field from
WinCC
.
All 30 S7-1200 have their own electrical panel and do their own process.
Note
:
We use DWords to save communication bandwidth between S7-1500 and S7-1200.
Also we use DWords to save Powertags between S7-1500 and Rack-PC supervisor WinCC
DWords contain statuses, faults, memories... (not only DI / DO)
Question:
As we need to send a lot of information bits between S7-1200 PLCs and the S7-1500, I suppose that IODevice exchange is not a good choice.Better to send / receive DWords ?
So do we need to avoid to configure our 30 S7-1200 PLCs as IODevice ?
Or to configure them (S7-1200) as IODevice doesn't affect SEND_C / RECEIVE_C communication ? What is more preferable ?
Is there a native way more suitable to exchange those DWords (contained inside external DBs of each S7-1200) ?
Thanks in advance,
David