Plinq strip separation and fragment separation?

In which scenarios is Range Separation a better choice than a Chunk section? (and poetic verse)

I already know that

• Fragmentation: capturing pieces of elements from input to the process, it starts with small fragments, increases the size of the piece.

• Partitioning determines an equal number of elements for each worker

Also why this code: (finding primes up to 100000)

IEnumerable<int> numbers = Enumerable.Range (3, 100000-3);
var parallelQuery =    from n in numbers.AsParallel()
                       where Enumerable.Range (2, (int) Math.Sqrt (n)).All (i => n % i > 0)
                       select n;

Can it do poorly with range splitting?

So far, this code: (finding the sqrt sum of the first million numbers)

ParallelEnumerable.Range (1, 10000000).Sum (i => Math.Sqrt (i))

Would it be a better choice for range splitting?