1080p and 720p won't make much of a difference. In case your cpu gets choked by 1080p stream, you can downscale it to 720
Put 'tick' to VBR (variable bitrate) and you can put it to 3500 and don't use custom buffer size
Set CRF to 5 (lower - better quality, higher - better performance, at least I think what that does)
Chose preset between veryfast and faster. The slower preset you select, the more cpu is used for encoding the video.
Select 32 samples(lanczos) in Video options
Also you can rightclick on your Gamecapture (cod2) in scenes and go over to scale filtering and put that to lanczos aswell so you minimize the watering/pixels on your stream
You should get clean stream and with that setup I don't think you will drop frames.