They should have IPs yes, but without a GW set.
I think It is better to have isolated vlans, the whole point of separating the 2 networks
is generally for this purpose, only data traffic traversing.
I am really tempted to try jumbo frames as well although the network I am under @ work is
not one I can risk playing with at the moment.
If you have time to experiment though, bumping your MTU from 1500 to whatever your
infrastructure supports will make a difference as well.