Actually if you have an SSD, saving FRAPS to there is probably your best bet even if it's already running everything else. You're not going to beat that speed.
Assuming you have room, anyway. FRAPS will go through hard drive space like mad.
Set your FRAPS video capture to full-size, 30 fps. You might even try 20 FPS or something -- I'm not sure what most videos end up being but you won't notice the difference between 60 and 30, at least. Going half-size will save you a lot of drive space but you won't get high quality full screen video out of that.