the heat is not actually that much of a problem unless you are extreme overclocking >4.4
There only few real life uses of pci-e 3, however my personal feel is that the next gen higher end cards will need pci-e3. So how long do you want your platform to last for. I expect mine to last for 4+ years and certainly let me run a GTX770, HD89XX
I'd go for IVB as then you won't need to (because you won't be able to) upgrade your chip until haswell.