You’re really just trying to lock in death points, and all else should be equal. L4 is only special in that it’s another chance to get a really big death.
Let’s look at some numbers. L4 only gives you 2 shots for an outlier score and L5 gives 55. Given that, you have a better chance of getting an above average score on L5. How much bigger do you need to break even and surpass L4 sacs?
Assume 14k L4 barrel average and 13k L5. They might be closer than that but we’re being hypothetical. Sacking on L4 will net on average 56k, (28 in sacs plus 28 in completions). With 13k L5 you only need 15k sacs to break even, and you have room to wait for a bigger one. Also, with 55 levels to choose from you won’t affect the average as much by stealing two big ones, where on L4 you can tank the start score with one bad level that can’t get washed awag as easily with large numbers of average rng/play.
So I stand by sacking the first 2 16k levels no matter where they are.