The ones on the 306 are crap. They are like a snail along the coast road, and was jerking a lot, and was ridiculously rattly.Haven't rode the 306 examples but based on the other examples I imagine they are crap.
Versas are much better, but Citaros would have been much more suited to the 4/X4 and 5.
The StreetLite's have been placed on the wrong routes they are better suited to local services and Arriva have instead decided to allocate them to long distance high speed routes which they aren't suited to and I imagine they will have big problems on these routes before long.
Mercedes Citaro's would probably be the best option for the X3/X4/4 and 5/5A especially although I think Pulsars would be okay on these routes.