The improvements that Ivy Bridge bring over Sandy are minimal, Sandy will be a viable architecture for a good few years especially if you're a casual user or gamer who doesn't require a lot of threads in your computing. I can vouch for the 2700k got one myself and they overclock like a dream, got mine from 3.5GHz to 4.7GHz without even a voltage tweak needed, great stuff!
Besides the deal you are being offered sounds pretty damn good! I wish we got deals like that in the UK. However, having said that do you still get the reduction on the motherboard if you purchase the 3770k?