Well, generic sticks of RAM have greater chances of turning up errors, and causing instability. They won't make your current sticks any more stable, but there's a lesser chance of getting a bad stick if you buy brand name. I'd personally go with brand name, as long as it isn't too much higher. If brand name is a lot higher, I might take a risk with generic to save some cash. Of course, that's up to you. You can always RMA it if it's bad RAM.
As far as timings go, a very simple explination is it is how fast the memory responds, in milliseconds. The lower, or "tighter" the timings, the faster the memory responds. Google it if you'd like more information.
As far as being able to change them in the BIOS, that all depends on the motherboard. If you have a high end ABit or ASUS (or something like that) motherboard, probably. If you have something more cheaper, or a non-overclocking board, then probably not.