1. You mean there's lag in the video but no lag in game? Not sure what you mean.
2. Like x264 above said. But I'd recommend using Xfire video record. It's allows you to record 30fps while playing whatever fps you want, and it uses its own XFR1 codec that is based off the lossless YUV, iirc.
Side question: when recording at 100fps, are you sure your ingame fps is actually at 100fps or does it stutter around like 30fps?