Even assuming python's foreach loop in these cases get optimized down to a very bare for loop, the operations being performed are dominated by the looping logic itself, because the loop body is so simple.

Each iteration of a for loop performs one index update and one termination comparison. For a simple body that is just an XOR, that's the difference between performing 5 operations (update, exit check, read array, XOR with value, XOR with index) per N elements in the one loop case versus 7 operations (update, exit, read array, XOR with value, then update, exit, XOR with index) in the two loop case. So we're looking at a 29% savings in operations.

It gets worse if the looping structure does not optimize to a raw, most basic for loop and instead constructs some kind of lazy collection iterator generalized for all kinds of collections it could iterate over.

The smaller the loop body, the higher the gains from optimizing the looping construct itself.