For video editing, the i7 is a no-brainer. Look for a high quality PSU from Corsair, PC Power & Cooling, Antec, etc... For i7, look for DDR3 1333 or 1600 RAM that runs at 1.65v or less. There are some pretty good X58 boards out now for around $250 US. I know newegg isn't an option for you since you're from the UK, but I'll link a couple just so you can check out the specs.
just looked at the cpu graphs and it does come in quicker up to a 3rd on somethings... but the motherboards and ram is sooo expensive, wont a fully spec'd p45 board and 16gb of ram with a 9550 be better than 6gb of 3channel ddr3 and the cheapest i7 chip?