I'll benchmark this tomorrow. The functional style makes reasoning about this segment much easier, since I can count on zero state mutation.

I'd like to see how the various Pythons hold up comparing:

```python
matcher = lambda r: applies_to(r, method, route)
return next(itertools.ifilter(matcher,
                              general_rates))
```

to 

```python
for r in general_rates:
    if applies_to(r, method, route):
        return r
    else:
        return None
```

and even a generator-based lookup:

```python
try:
    return next((r for r in general_rates if applies_to(r, method, route)))
except StopIteration:
    return None
```