Doug, is there anyway to get access to these ?
Note: I already have the IQ280, so this will only be for affirming how much I can push it in the field.
Thanks
Shoot me an email with what you're looking for and I'll send them when I'm back from a personal trip I'm on at the moment.
In general I'd suggest ISO35 @ 20C @ 100 seconds is the start of the strong rolloff in quality on that back. The rolloff is still modestly acceptable at 120 seconds (the official spec) but quite far gone by 140 seconds.
This only applies if you wait a few seconds after a previous exposure (for any heat build up to dissipate) and only in normal latency.
It also only applies when using Capture One for raw processing since the most noticeable increased noise comes in the form of stuck/hot single-pixels which C1 can handle better than LR or ACR.
If the ambient temperature is significantly lower you can push a good bit further. If the ambient temperature is significantly higher you can't get anywhere near these numbers.
It also depends on what you find "acceptable" - there is no right or wrong here. Even a 10 second exposure is not the same as a 1/100th exposure regarding noise - in my eyes (and the eyes of nearly all customers I've worked with) the change is subtle enough that it can be ignored, but not in all eyes. This is especially true as the most immediate change is the loss of pliability in the file - the default presentation could be quite similar, but add 40 points of shadow recovery and the shorter exposure shows it's strength.