No values for Soyuz or Dragon on wiki splashdown page, but the lake listed for the one Soyuz water landing seems to be like 20x40km. NASA shows the Soyuz landing zone as 25km wide.
There is a thread on NSF where the users posted some graphs of landing accuracy, one of them showing the SpaceX COTS-1 and claiming the precision (0.8km) was much better than average Soyuz and even better than the best of Soyuz TMA-04M (2.2km):
user Comga, forum.nasaspaceflight.com
For Dragon landings there is a map posted by reddit user Raul74Cz but no hard numbers in there, only estimates based on reentry areas (which - being the expected worst case - are quite big). I was not yet able to find some exact values for other Dragon landings, articles only mentioning the landings being "precise" with the recovery vessels being "near" the spot and quick to get to the capsule.
2017-03-19 this image was tweeted by SpaceX
It shows the CRS-10 Dragon capsule still in the air being photographed by the recovery crew. I found no data about the focal lenght or similar which would allow to estimate the actual distance but it is visible and does not look too far. Taking into account that the recovery vessels probably stay out of the designated zone, it may be just a lucky coincidence but it being not a first such photo suggests it is not just random chance.