Cliff has always had certain tricks he's applied to the stock internal IRs, like somehow removing the sonic artifacts of the mic used to take the IR so that we can use mic sims effectively with the stock cabs.
Actually, that's not completely true.
I/we don't really know everything that Cliff does to the IRs that are included as stock IRs with the Axe II.
Me saying that basically relates back to a previous fantasy I had of how I thought the majority of the stock cab IRs were done but also to my experience with the now #119 stock IR as detailed below.
Most of the stock IRs that do not have a qualification that they are OH or RW IRs were shot with a TC30 test mic which is flat enough that you can consider it to have no mic coloration at all and makes these IRs suitable candidates for further processing via one of the Cab Block's mic sims.
But I know of one stock IRs that breaks that mould though, #119, the 1 X 12 E12L (V9) IR.
This IR was originally at #8 in firmware 9 and then was removed in firmware 10, but a few users such as myself missed it.
At first Cliff just posted the .wav file and the .syx file from which that IR was derived and it's called "EVM-12L KM84-3in".
Eventually he put it back in a later firmware update where it still resides now as #119 "1 X 12 E12L (V9)".
My understanding is that it's a RW IR taken out of the Speakerbox EVM library.
I own that library too.
There isn't an IR file in there with that exact same file name ("EVM-12L KM84-3in") but there is one called "EVM-12L-KM84-Cap-3in" and I've always assumed that the file that Cliff posted and the file that was used for #119 started out as this same RW file.
But the two IRs sound quite a but different.
The raw RW file is brighter and does not take well to using any of the mic sims.
But both the file that Cliff posted and the #119 cab type DO take the mic sims quite a bit better.
So, either Cliff really has done some sort of post-processing to this IR (e.g. simulating the removal of the tonal coloration of the KM84 mic) or the raw RW file that I own is not the same file.
So, I'm not really sure if Cliff has some magic voodoo he applies to his raw IRs before he loads them into the Axe's stock cab types slots.
But I suspect that he does do something like that with at least some of the stock cab types.
So, again, this makes me wonder if UltraRes IRs created and marketed by Fractal might wind up as being superior in some ways to UltraRes files acquired by some other means.
But I'm just thinking out loud here and am playing devil's advocate.
There's probably nothing to worry about at all with creating our own UltraRes files with Cab Lab and a suitable .wav file.