You have the antec 300 black linked, not the 300 illusion. The illusion is the same case with the two front fans already installed. Without those front fans it wont have the same airflow. (Or you could buy the 300 and a 120x25 fan to install in the front). http://www.newegg.com/Product/Product.aspx?Item=N82E168...
The 5850 is only a 9 inch card so it will definitely fit.
How do you know? They only tested 5 brands and that was just testing. And it not only fried the board, it fried the processor too.
How do you know the other brands wont fail too at a later date? Theres been a ton of posts here the last few days about overclocked i5's that worked fine for a week or two and now they wont boot or they crash.
These boards are built on Intel spec and I would hold off on buying any of them. If your blows due to overclocking, they are not going to replace it.
And it wasn't just 1.45v, one of them failed at 1.36v.
I guess it is a good thing I am waiting until the end of the month then. Hopefully by then there will be more information on the matter. For now I will just pickup case, psu, GPU and such that are unrelated to P55.