I'm actually glad I didn't decide to sell over my 5850. All the rumours lead to the conclusion that whilst a 6870 will be faster than my 5850, I would expect it to be in 10-15% margin that can be easily narrowed to 5-10% when overclocking (5850 has a massive headroom for it).
I currently run my Radeon at stock and TBH there's not much more performance I need at all. Let's have a look at what I play atm, Age of Empires 3, Bad Company 2, Dirt 2, FIFA Online/11, Left4Dead2, M&B Warband, Napoleon Total War, Civilization 4 and 5, SW: Empire at War, Test Drive Unlimited 2, The Witcher, Tropico 3 and World of Tanks. NONE of which require more power, also, I haven't encountered many games that would and none of them had lasted more than a few evenings anyway.
I'm pretty sure 6850 and 6870 will be great cards at their price range but upgrading for me would require a lot more money than I really want to spend on my PC and wouldn't give me any noticeable benefits. I may as well wait for a bargain second-hand 5850s that will probably be selling at £120 in a few months. Still, looking forward to first benchmarks and reviews, this is going to be an exciting year.