All of the batteries I use in my larger models are 35C which I think I arrived at when researching when I first got into the hobby.
Problem is that most manufacturers overstate the capacity of their batteries, though the better brands do it less so. But even for them the reality is probably that the capacity in use is less than that stated due to what I mentioned earlier, the internal resistance. Whilst your figures were very good some of the power is still being used to provide heat (all batteries heat up to some extent when being worked). One of the links I posted earlier, the detailed one, says that the actual capacity can be a lot less than the manufactures stated and so like with an ESC it is better to err on the higher side I think.
It's interesting that they quote a range of 20-30C rather than a fixed value like other manufacturers, wonder why that is?
I think the bottom line though Bob is that you now have replacement batteries and the existing one is always going to have a question mark over it in your mind so the best course of action is to dispose of it.
At least with the new ones being stated as 50C you have some leeway. That's what I was going to get for my Swordsman as it needs a 4S and being a bigger heavier boat than my others and requiring a higher rated ESC then components are going to be worked a bit harder.
Chris
Edit: Did a search and this was the AI response. And this from Overlander Batteries.
https://overlander.co.uk/understanding-c-rating-how-much-power-does-your-rc-need/?srsltid=AfmBOorrB2PDzzkfQNsfYcLrhkV4nKw2HfLwjSE3VOEc3llT26Hpl0Gf
Scratch building 7 Faireys at a scale of 1:12 and also have 2 built by Dave Milbourn