I think it depends a lot on the other details, especially how expensive the extra GC will be vs the wasted space. Hard to give a rule that will work in all contexts.
In our case, it wasn't a single hard-coded number - the input data gave us the upper bound, and the difference between the upper bound and the median case was so small that going with the upper bound worked out best.
In our case, it wasn't a single hard-coded number - the input data gave us the upper bound, and the difference between the upper bound and the median case was so small that going with the upper bound worked out best.