dependent on your client devices primarily, VBR is going to be more bandwidth and storage efficient than CBR.. however encoding and decoding VBR for playback requires more power than CBR.
If your camera or playback devices are struggling for resources then see if CBR helps alleviate some load, otherwise VBR should be be better.
Frame Rate: 15, tops.. more frames = more storage space, unless your needing clear photos of cars passing at highway speeds, 20-30FPS is typically far more than you actually need.. pick a number divisible by 60 that gives you an even result, which is the standard for HD so you dont get any 2:3 tearing, thats what screws up motion's smoothness... 10FPS or 15FPS are the most common depending on activity you can even go lower and get pretty good results.
