I've been paying attention to what the sites for Thudersky(from when they were ThunderSky), Winston, Sky Energy, CALB, Sinopoly and HiPower have been saying.
ThunderSky never had a time frame on their short term 10C discharge but always said 3C constant discharge. ..this was when their 1C discharge chart showed plenty voltage sag to where under 3C they only got to about 40% SOC before dropping below 2.5v.
Winston current specs below, same thing for every cell, see what I say about Sinopoly below. The C ratings should be different for different cell sizes as the voltage sag is different but Winston battery charts are questionable because they take the exact data and put it on every cell size.
Sky Energy and CALB have showed specsheets showing 10 second short term discharge at 400 amps for 40Ah cells, 600 amps for 60Ah cells, 700 amps for 70Ah cells, 800 amps for 100Ah, and 1000 amps for everything over 100Ah. I have yet to see a CA specsheet that was updated recently and this one is old but can be obtained if you can handle Chinese the way I can and track down the PDF file on their site, which it seems nobody else has. I haven't posted it to this forum because it seems outdated based on what's in it and that it hasn't been changed in the past 2 years or so but here you go.
Sinopoly says 5C all around for everything from their 40Ah
to their 1000Ah cells
This doesn't make much sense to me and I think their 40Ah is probably just as capable of 10C and discussed their 20Ah cells via email with Sinopoly and they said they could be 200amps discharge with no problem for 15 seconds but hadn't shown the test results anywhere.
There was a document here showing voltage sag of 5C discharge from Sinopoly 100Ah cells and I think they could easily do more than 5C for a short period without overheating. This is just my opinion though and I understand why they might be cautious when creating specsheets.
HiPower their cells used to be geared towards lighter weight which they had some of the lightest cells you could put into a car but their discharge rates used to be the lowest amongst the prismatic that we could get here. They have since redesigned their cells and they seem to be much better at 3C continuous and 5C 60 seconds and 8C for 15 seconds.
Wayne Alexander of ev-blue.com has been putting them into cars(recently saw a Saturn conversion in Wisconsin and spoke with the owner) so he must have a distributer and it might be worth asking him where he gets them.
I hope this helps, please keep in mind I haven't tested all of these cells and am merely commenting on data from specsheets and from the information that I know of people who actually have used these cells.
For Winston, ThunderSky, and CALB data there are charts from Jack Rickard showing the whole discharge. Simon showed incredible performance of 1976amps at only 2.74v sag from new 180Ah CA series cells. As far as Winston goes, I'm very curious to see something from Jack Rickard's 400Ah cells but I have a feeling I might not see any data from them unless he does a dynamometer test on the Escalade, which seeing as he has done the rest of his vehicles, I'm interested in seeing that too.
Voltage sag shows a direct correlation of the internal heating inside the cell, the less voltage sag, the less total internal heat created in a cell. IMHO if you can keep your LiFePO4 above 2.5v on a 10 second discharge you are in good shape for those 10 seconds. Obviously you don't want to be discharging a high rate from your cells and then pull down to 2.5v for 10 seconds because heat is cumulative and takes time to dissipate. If you are under 50C consistently measured directly at the cell terminals, I think you are in good shape for long cell life, again IMHO.