Opinion
This is my opinion, the old argument about lighter vs heavier break cues:
To say, you can stroke a lighter faster, yeah, considering the length of the stroke, maybe 1 mph faster if that. A few ounces is not going to make that much difference. What matters is your stroke and strength to begin with, that determines your range of force on the cue ball. yes, getting your body weight into it increases the force, something a lot of players never understand.
Get what is comfortable for you to have. If you aren't strong for your size, a 19, 20, or 21 might feel heavy to you. If you are strong, a less than 19 oz. might feel like a toothpick to you.
I have tried light Break cues, and it always felt like I was hitting the cue ball with a straw. Mine is 19.5 oz. which is comfortable for me. My playing cue is about 20 oz.
Oh, the Dr. Popper jump cue, from what I have been told, will get up in the air, but accuracy is a problem.