[Neil H]

Actually only the PCIe core card is the only card that's more powerful because they made them into accel cards.

So PCIe systems consist of an Accel Core and then Accel cards.
A PCI system consists of a non Accel Core and Accel cards.
You can also use the older non Accel PCI "process" cards that have the same DSP as a non Accel core but I wouldn't bother as it's a water of a PCl slot and most of the TDM plug inside were updated to require accel processing so a process card would be next to useless.
You also want to be careful just fully loading a system with cards because bandwidth can quickly become an issue on some motherboards I would say go with an HD5 to start with and see how that goes before investing in more cards.