Something like this?

```python
resp.stream = my_file
resp.block_size = 16 * 1024
```

So, if I have to do that a lot in my app, it could become tedious. How many apps will want to change block size on the fly?

For sake of comparison, we could instead (or in addition to) the above, allow setting this at the API level. I probably wouldn't make it a kwarg for the initializer, since I don't imagine it is going to be used that often, but instead just have the app set an attribute if they want to override the default. But then we need to consider the possibility of other options in the future, so we would have to think about namespacing:

```python
api = falcon.API()
api.options.resp.stream_block_size = 16 * 1024
```