Few points:
* engine 1.0 doesn't support the new QVM format from ioQuake3 SDK so you definitively can't use new PK3 since v1.1b1 with SG 1.0 engine
* As far as sg_pak1.pk3 is updated, you won't be able to connect on updated online servers unless you have auto-download feature activated on server and on client (like it is on current beta servers). When autodownload is activated, your PK3 is auto-updated to latest version. If client didn't activate auto-download, he will fail to connect with a pretty and clear message.
Btw the binary itself from previous beta could be used, but this is up to the client to update this program. And you should know we have activated "update" and "authorize" server tools, so we should be able to help admins to reject not up to date clients if it's really important.
Not updating engine is less critical than not updating PK3. This will essentially mean you won't benefit from features like FBO effects (bloom & rotoscope) is you don't have at least v1.1b3 engine... Updated engine means essentially better engine features support.
So don't worry