You can't put these heat sinks on the ram on the video card. You'll be fine overclocking the ram, you'll have a bit of head room. Just do a little research on it maximum tempatures and watch things closely. if your only overclocking to 2.6GHz I wouldn't even bother buying any ram coolers, but thats up to you. Don't worry about the northbridge it should be fine, your not straining it much at the clocks you showed me.
In the end just read, read, read, read and read some more. I'm just introducing myself to overclocking so those questions should be addressed to someone else.
Also before you overclock research temperatures on every piece of hardware you plan on overclocking. And if your overclocking your video card, your more then likely going to be overclocking the ram on the video card, it goes hand in hand mroe or less.