I love your story of starting out on pace and then reeling in the others as they fatigued. That is the first strategic principle we want to employ. And it worked for you!
Later on, when you are in more competitive field of swimmers or a more technical course, you might work on variable pace over the course of a swim.
5K to 10K Pace
I believe it is known in elite distance ow swimming that 100m pace tends to drop off dramatically from 50 sprint to 1500 distance, but then it nearly levels out from 5k and beyond. Swimmers don’t necessarily swim slower, but they need to train in order to last (at that pace) longer.
So, you are on the right track with holding a steady pace.
And, the practice pattern you followed for 5K is essentially the same for 10K. We just increase the volume per week, particularly in the distance swims.
To get an idea, look at this (attached image) calculation I made for a swimmer who is preparing for 20K. I took the 10K training plan distances and added additional volume per week at his stage in the training plan.
Attachments:You must be logged in to view attached files.
~ Coach Mat