I'm going to lay it out simple for ya
The first thing to do is use software like bandicam (as you do already). Other good ones include Fraps and Action! or something like that.
Recording live is great for commentary if you're going to be doing that but if your computer isn't really powerful it's going to be hard to get an FPS you can play at (for example 125) and be able to record at the same time.
So you can go that route OR as @@Michael / ExclusionsHD mentioned, you can record via demo. To put it simply, it's recording your screen however in a format only the game can view.
Recording demos don't really impact the FPS because you run the demo after you've played and it's like recording a video and you can record at 30fps since you're not playing so you do not need 125fps if that makes sense. This still means that you have to use bandicam to record the demo but you'll get good fps while playing and you can make your videos unique with the use of special textures or configs.
But, it means you can't live commentate however there is a work around. You can record audio only while your playing and in video editor of choice (Vegas Pro 11 for me) add the audio to the recorded demo.
The only problem is that it causes a bit more work to be done and the audio might not match the video. For example, you might scream "NOOO!" when you die while your playing and then when your editing you have to match up the place so you say "NOOO!" at the right time. To remedy this, do an audio check at the start so say "1" and shoot your gun and then "2" and shoot it again, this will make it obviously where the audio should meet up. If you're not commentating this isn't a problem. Also demos include ingame sound like gun shots so don't worry about that in editing.
The last and easiest way is to buy an EXTERNAL capture card (or internal if you're using a desktop PC). This works similar to how you record on a console (ps3, xbox etc) but it's on the PC. A popular one I know of is the Live Gamer Portable by AVerMedia. The upside to this is that you will get NO lag at all and NO compression of the video which means it's the same as if you were using fraps on a super powerful rig etc. It has no lag because all the recording stress is sorted by the capture card and not your computer so it means that there's no lag!
The only problem is that it costs money but if you're getting good at YouTube and you're growing but you want higher quality and good FPS it's the best route to follow.
Hopefully that makes sense.. It's all very complicated.
If you want more information on demos (if you're going to do that) pm me or reply and I'll tell you how to sort everything and even run better graphics configurations or cool textures etc. Also, there are always tutorials on YouTube ;)
p.s if you want to improve performance ingame, turn down settings, turn down anti aliasing, turn down game resolution, run fullbright etc. However I hate watching videos with fullbright because it makes your game look ugly. HOWEVER, you can use it if your gonna do demos since you can turn of 'r_fullbright' while running the demo so you can experience it while playing but not have to have it in your video if you know what I mean :S