TCP connections offer in-order reliable delivery so you shouldn’t be getting any data out of order.
But you do need to be careful because even if you send 512 bytes, for example, there’s no guarantee that the server will receive 512 bytes at once. Often they will but it’s not guaranteed. They could get 212 bytes, then later get another 300 bytes, in any quantities. In other words, the chunk size you write is not guaranteed to be the same that the server receives.
So even if you could write several K at a time with client.write() it still wouldn’t guarantee that the server would get all of the bytes at once.