[ffinder]

код на F# с аллокацией и одновременной инициализацией массива:

open System
open Microsoft.FSharp.Collections;

let finalValues =
    let arrSize = 512 * 512 * 128
    let start = 19 * arrSize
    seq { for i in 0..arrSize-1 -> start + i } 
    
let enumerator = finalValues.GetEnumerator()
let getNext _ _ _ = 
    enumerator.MoveNext()
    enumerator.Current

let timeBefore = DateTime.Now
let yobaArray  = Array3D.init 512 512 128 getNext
let timeAfter  = DateTime.Now
printfn "Allocation and init time: %A" <| timeAfter - timeBefore

Console.ReadLine()

результаты:
Allocation and init time: 00:00:13.5615343