AFAIK no no difference at all. I think it is more a bandwidth thing. PCIe has more bandwidth but since PCI is enough for the HDSP9652 it won't make a difference.
Latency is a product of the buffer(size), not the PCI(e) speed.

Thanks for all the replies. By offloading I was thinking about, if the DSP chip of the newer model cards is off loading even more of the routing mixing processing, than the older cards?

Regarding buffer size, I know how it is related to latency. But I was curious about RME's statment of "even lower latency"...
Like do the pcie have any humanly noticeable difference compared to pci. PCIe have dedicated none shared lines to the cpu, that is something pci do not have. And that is a good thing for uninterrupted audio. But does it matter? Do pcie run more smooth than pci?
I do have a motherboard with both pcie and pci, this is a dual xeon board, but I can not get it to run stable with latency lower than sample rate 48, buffer size 128.
As I have written before, even if you can get a faster more modern cpu, a good optimized system is still key to stable performance.
But a newer card is also double the price....