Updating server to 1.0.4

Hello again.

Currently our Xibo installation is using 1.0.3 server & clients (15 clients right now).
I've noticed lately that server is more & more overloaded, specially when adding new clients - during files sync.
Last 2-3 clients even refused to sync server and i've to apply apache2 reload to force server to send layout correctly.
I'm guessing that because server need to calculate md5s of ~200 big mp4 files every time.
So i would like upgrade installation to 1.0.4 version.
But some of clients are installed remotely (some of them turned off right now etc), and it is quite hard to update them in single hour/day - just after updating server.

So my question is: Would 1.0.3 clients work with 1.0.4 server? No, i guess?
If no: there will be any visible sign of version mismatch of terminals screen before updating them? I hope those client would keep playing last synced schedule plan/layouts from 1.0.3 server?