If Sandybridge is hot for you then just imagine about Ivybridge which gets hotter than Sandybridge. This is the reason I am saying Sandybridge would be better. The advantages of Ivybridge is not worth it,
PCle 3.0 native support - We haven't even reached the speed of PCle 2.0 speed threshold.
USB 3.0 Native support - Sandybrige performs better with USB 3.0 speeds rather than Ivybridge.
10% performance gain - You can overclock Sandy more than Ivy to get similar or better performance without problems.
Nope.Though there can be some anomalies but in general it is not true.
Z68 chipset motherboards which had usb3.0 used 3rd party usb3.0 controllers like asmedia usb3.0 controller.
Z77 chipset mobos have both Intel® Z77 chipset usb 3 and 3rd party usb3.0 controllers like ASMedia® USB 3.0 controller.
In reviews(both in CrystalDiskMark and HD Tune) it has been seen that the Intel Z77 USB 3.0 Controller is quite a bit faster than the asmedia and other 3rd party usb3.0 controllers which is quite reasonable as Intel is native whereas asmedia is used as an add-on chipset which adds to latency.
Overall though the difference in speed is not that much as of now.