Http://cooking.stackexchange.com/questions/33540/does-a-head-of-lettuce-really-need-to-be-refrigerated gives a table showing that leaf lettuce at 10 degrees C evaporates only about 30% faster than leaf lettuce at 5 degrees C. That difference isn't that large.
It also gives head lettuce at best two weeks at five degrees centigrade. So, two weeks at 10 degrees seems a good result.
On the other hand, the article says _about_ two weeks; they might mean 'ten days plus', and 'freshness' may be highly subjective (I bet there is a standard for measuring lettuce freshness)
