Paper launch with whatever A3 silicon they get back might be sometime late January, there won't be real shipments till 2 months after that at the absolute earliest.
April/may seems the odd's on bet, but theres something few people are mentioning yet, and thats IF the A3 silicon is good enough, even Charlie doesn't suspect it won't be as yet.
It will be better availability than the 5870 right now this second, but worse than the 5870 was at launch and in a few weeks. its a much larger core, its yields will be lower than a smaller equivilent, meaning if AMD get say 100 cores off a waifer, Nvidia will only be getting maybe 55-60 ish. So production will literally be slower when a core is 50% larger, you can't get around that. A Fermi will also have a more expensive core, pcb, 1.5gb gddr5(I'm assuming AMD get better prices off Samsung and Hynix for it because they invested millions in its R&D and co own a lot of patents on it) so unless Nvidia take almost zero profit, I can't imagine it being anything less than £100 more expensive.
What we really want is Fermi's mid end parts to come out, smaller core won't offer any benefit over AMD's parts in terms of price, but on a mid end part they should drop to a smaller bus, a lot less memory and a hugely cheaper PCB which are the things that cause Nvidia's high end to be that much more expensive. If Nvidia can at least offer some price competition around the 5770 that should bring some price cuts around there, which will also cause a few price drops above it aswell. You can't sell a 5770 for £100, and a 5850 for £200, you need something in between, either a faster 5790, a 5830, or price drops on the 5850.
Problem is we have no clue when Nvidia will have a midrange part coming.