Thanks for the tutorial, I'll have to give that run a try.
As for the grainy video, I think that's in the video encoding. Go into OBS->Settings->Encoding and find Max Bitrate. I think it's something like 2000kb/s by default. Raise this to something like 8000 or even higher if you've got the storage for it. You'll have to find a nice balance between quality and acceptable file size.