Ivy Bridge itself is what supports PCIe 3.0. You can get a non Gen3 mobo and it will support IB but not PCIe 3.0. You need a Gen 3 to support PCIe 3.0.
IB won't be a big change it's n incremental change not an iconic change
I wouldn't expect much more
Pci 3.0 has no usefulness at the moment
Actually PCIe 3.0 is a major change itself as it removed the requirement for 8b/10b encoding.
IB is showing around 1.5-2x the performance IGP and 10-15% better CPU performance.
Personally you can just go for a SB system now and be perfectly fine for the next 3-5 years.