The performance-part is quite sef-explanatory: The new CPU has more core, but less frequency, so any single-thread performance benchmarks (and this is the most real-world-usage) is worse. Most VM system I've ever seen make exactly this mistake and ask then why the performance of application xyz is not good. Yes, you can virtualize a lot more machines (if you really need the CPU power), with a CPU that has more cores, but the overall performance is always decreased and most of the time, you're limited in RAM anyways.
Is this screen tearing with PCIe passthrough?