Regarding P55 and PCIe, that isn't strictly true RJL65. All PCIe x1 sockets are connected and use the PCH and don't steal lanes from the two main PCIe x16 sockets.
Sound cards, tuners etc etc, only ever use PCIe x1 in my experience, so unless the user wanted Crossfire or SLI, then yes, each card would only run at x8. But then again, PCIe x16 on P55 is onboard the CPU package itself, and much more efficient and has much lower latency than the arrangement on the X58 chipset. Not to mention it uses much less power. The i5 is also a cool running chip as it has no HT, and overclocks very well.
In the benchmarks that i have seen, the i5 750 is faster than the i7 920.