Break cue
I played with and broke with a 21 oz. cue for years (30+). I used to get comments about how much my cue bowed when I broke. I, now, play with a 19 oz cue, and my J&J break/jump cue is 19.5 oz, so I guess that puts me in the camp of being close to your playing cue's weight.
It works for me, and I like the feel of slightly more weight for my break cue. More importantly though was the switch from breaking with my playing cue over to a break cue. I feel the 13.25mm shaft on the break cue is a big improvement over the 12.75 mm shaft on my playing cue, plus the difference in tips on each.
If you have a nice playing cue, you always are afraid of scarring it up on the break, and that plays with your mind some. With a break cue though, it is if it works, and not the looks so much. A few dings on a break cue don't matter.
I don't give much creedence to the lighter is faster theory. Even if it is, the difference is so minimal that I do not feel it would provide that much difference from a heavier break cue. I, also, feel a slightly heavier break cue helps for tracking your stroke on the break.
Years ago, in Vegas, I had my break timed 3 times, and I broke at 26, 28, and 31 mph.