Nice efforts!
They are a real challenge.
All the successful ones that I have seen have a shutter speed of 1600 or faster, and I think they have been captured during their glide phase. (I see that even your fastest one failed to stop the wing movement.)
I am currently trying to get clear shots of them (mostly tree swallows and purple martins) skimming and diving into the lake. They tend to be 50-100 feet away and feed mainly at dusk. Under those light/image-size conditions it's difficult to get an image that's large enough to crop and enlarge.
But it's nice to sit out at the lake and watch!
