What is the cost of this combination? The E450 is nice for a low end system because compared to an intel onboard gfx its a lot stronger, however if you're going to get an Nvidia 560 or any discrete gfx solution, it defeats the purpose of going for an apu, and believe me I have a E350 laptop, the cpu is very weak(equivalent of an atom), any sandybridge cpu will get you a lot more powerful system.
I would take the crappiest i3 21xx over the brazos platform any day if you dont plan to use the gfx part of the E450.
just a random test to show the difference in cpu power. Check out the rest of that article as it focusses on the kind of system you have in mind. (the E450 is maybe 10-20% more powerful but still very very weak)
If you want to go for an APU look at an AMD A6 or A8.
If i'm reading this totally wrong and the cpu you're planning to use is not an E450, then nvm anything i said.