Hi Chaps, interesdted in opinions on whether having both parity disks on the same controller is a good or bad idea? in terms of write speed?

Depends on the bandwidth available to the controller.

lets say for the sake of argument we have the motherboard in built sata and a PCI E controller

I use motherboard sockets for parity and cache disks. Any remaining I use for data disks, and then I use PCIe cards for more data disks. That's a simplistic approach though and on some motherboards some SATA ports can be better to use than others. It depends on the specific architecture. The more detail you provide of your specific situation the better the replies will be.