Setting MTU

Hi,
can anyone tell what is best MTU values fro best perfomance in this configuration :
two Mbox over wifi (prism 2.5)
each router have this setup :
WIFI>WDS>PPTP>EoIP(Bridge)Eth

What is best MTU values for each interface to prevent packet fragmentation ?

Thanks a lot for help

/Tomi

Any ideas ? :frowning: