Pulsar 2 is 6DSP chips. After adding the XTC to your P1 you'll end up with 10 DSPs so it's more than Pulsar2 But if you mean lower ULLI settings then yes, adding a second generation card (XTC is such) to your first generation card (P1) allows you to have ULLI at <13ms at 44.1kHz
definetely not - I once asked the same question about exactly that configuration on CWA's supportline.
the latency IS set to the lower value, but the physical IO (if any) puts some extra load on the system. We didn't get into more details about the latter, tho.