> You could always test it

Ah the joys of unexpected results. Scrap that then...

```
In [12]: 
import numpy as np
bin_file = 'delme.bin'
txt_file = 'delme.txt'
with open(bin_file, 'wb') as fh:
    np.save(fh, np.arange(120000., dtype=np.float32).reshape(300, 400))

with open(txt_file, 'w') as fh:
    fh.write('Testing multi line\nASCII file\nI wonder how much slower this really is...' * 1500)

In [13]:
%%timeit
with open(txt_file, 'r') as fh:
    fh.readline().strip().startswith('Testing multi')
1000 loops, best of 3: 302 µs per loop

In [14]:
%%timeit
with open(bin_file, 'rb') as fh:
    fh.read(4)

1000 loops, best of 3: 299 µs per loop
```