Nice shots Dermit. It can be a battle trying to get the right exposure with sunlight reflecting off water (not to mention getting focus on a face with water trying to grab the attention of autofocus).
One backstroke shot worth trying: shooting from the end of the pool opposite the starting blocks at knee level, capture the surfacing of the swimmer and their first stroke. When they are just a few inches under the water surface, it is a pretty neat effect and their first surfacing stroke tends to pull them out of the water a bit and can be powerfully dramatic compared to most backstroke shots.
I think starting shots work better at a wide angle to give it context. I've seen some interesting starting block shots where one track's a single swimmer, and bring the shot speed down which will blur everything around them. You may only get their head and shoulders in focus, but if you get lucky it can be a pretty neat shot … this works particularly well with a 70-200 lens. I've seen it shot from both a very low angle (under the swimmers) and from a slightly higher angle.
I don't know what your keeper rate is but I've found that slowing down the AI servo tracking speed through custom functions can be helpful.
Keep up the great work!
Tim