Out of all the models you listed, I would say the Emperor BB and the Geier bomber are the two that I have found most useful. These two units can be pretty strong on their own, which is important since you are mixing and matching and as a result are losing out on some of the synergies of the PE. If you wanted to buff your other PE units some, the Speerwulf is probably your most cost-effective option to bring in some Speerschleuders.