i think its best to deploy all under 4.8 with ADNM....
the new server will function as the AMS server (ADNM) and updating definitions and program will occur from a single point in the network.
this way your internet connection is not hampered every xx minutes from all the avast clients checking for updates and downloading updates separately, this will be done only by the ADNM server and the avast client traffic is only on your highspeed local network
all clients (except the v5 one, remove this first with the removal tool) can be push installed with 4.8 managed client (yes u need to push the managed client over the normal 4.8 installation).
Assuming Avast software has created the upgrade possibility of 4.8 managed clients to the new v5 managed client you can then push the v5 client over the 4.8 client and do your joy dance
This way u comply with the guidelines set by your company already (centralized managed solutions).
but that is from a control point of view....
There is also the posibility to put the 3 new machines in test with v5 too and wait for the new v5 equivalent of ADNM. Tho its totally unsure when it will come out, the blog mentions a hope for summer 2010 but a hope is not something sure.... which means you will have to run with a decentralized unmanaged AV sollution for the time until the new software comes out. When it comes out you probably have to manually remove avast from the stations (its what i would do in such small enviroment) and push the installation of the newest managed client to the stations at once and your done....
The downside is that all the clients check on internet for themselves for updates and individually download updates for definitions and program, meaning 20 times more internet traffic usage then when using a central server that downloads the updates
with these scenario's i assume that all computers are in the same building
i believe the questions here would be:
1) can we wait with updating to the newest ADNM v5 version for centralised management of AV sollution or not
2) if not, why can we not wait? (if this is a crappy reason like "we like to see all the icons orange" then u can wait)
3) how strict is your policy to centrally manage adnm at this moment. Clearly the new software is not here yet but its coming. you are protected at this moment so how mandatory is the policy to centraly manage something
edit: i started typing this 5 hours ago but i got disturbed and had to go into a meeting until now