[There was a warning that you should not push Float64 into a DataFrame? I changed push!(df, k)to push!(df, (k,)) and the warning is gone.]
One point?
julia> do_stuffdf(50)
50×1 DataFrame
│ Row │ k │
│ │ Float64 │
├─────┼─────────┤
│ 1 │ 6.09514 │
│ 2 │ 6.186 │
│ 3 │ 6.27277 │
│ 4 │ 6.35558 │
│ 5 │ 6.43461 │
│ 6 │ 6.51001 │
│ 7 │ 6.58192 │
│ 8 │ 6.6505 │
⋮
│ 42 │ 7.7578 │
│ 43 │ 7.76985 │
│ 44 │ 7.7813 │
│ 45 │ 7.79218 │
│ 46 │ 7.80253 │
│ 47 │ 7.81236 │
│ 48 │ 7.8217 │
│ 49 │ 7.83059 │
│ 50 │ 7.83903 │