Subjectively, small-to-moderate. Quantitatively, from Figure 1 of the (paywalled) journal article: Correct recognition of words as studied/unstudied was 77% for read aloud, 74% for hearing a recording of oneself reading aloud (from a session 2 w previous), 69% for hearing someone else reading aloud, and 65% for reading silently.

Although assessment was done with a recognition task, previous work in this area has shown a similar effect for recall tasks.

http://www.tandfonline.com/doi/full/10.1080/09658211.2017.13...