This is a selection of articles which were saved at FAR over the last few years. I've used the current word count, given that the FARs were all reasonably recent. Double checked a few to see if there was a systemic bias towards lead changes, which there wasn't.
Combined with the December 2022 set, 10% percentile is 206 words, 90% is 488 words, the 5% is 185 and 95% is 523 words.
For sentences, the 5% is 7, 10% is 9, 90% is 22, 95% is 23.
Conclusion: let's say that leads are often between 200 and 500 words and sentences 10 to 20.