I'm guessing you're talking about gaming capture/recording?
You want a dedicated, seperate HDD for recording/capturing video. Don't use it for anything other than the raw video captures.
You want as many cores as possible (4-6 or even 8) and relatively quick RAM (1600 or 1866 is plenty) for streaming.
And use good capture software. For newer intel CPUs with QuickSync, Myrillis Action is great for file size and CPU overhead. Fraps is also great and one of the most mature products for capture. MSI Afterburner is FREE and also very good, but I consistently get better FPS with FRAPS. Another option worth testing is DXtory, which is more complex but worth the effort if it works well for you.
What resolution and settings are you playing at? Dxtory is a nice one that allows you to record at a specific fps and won't cap your frame rate when playing. Say, I want to record at 30 fps but play at 60, dxtory allows that. Also, you might want to upgrade your CPU.. And get some ideas from the guy above me since he knows a lot more then me.