It was bugging me that I couldn't remember the details so I looked it up on the
Wiki.
The Cab block has 3 resolution modes: Hi/Ultra Res, Normal Res, Stereo.
Normal Res: supports IR consisting of 1024 samples. You can often use Normal Res without any negative impact on the tone, compared to Hi Res.
Stereo: supports two Normal Res IRs. CPU usage is the same as in Normal Res mode. Stereo mode does not support Ultra Res IRs; to use Ultra Res in stereo cab modeling, you need two Cab blocks in parallel, with their Input and Balance panned to each side.
Hi/Ultra: supports Hi Res IRs (2040 samples) as well as Ultra Res IRs (up to 8000 samples). Using Hi Res or Ultra Res IRs requires more CPU power than Normal Res / Stereo. But Ultra Res is more efficient than Hi Res, which results in about 4% LESS CPU usage with MORE resolution.
If you don't need cabinet simulation at all, for example because you're using the Axe-Fx II for effects solely or exclusively with a power amp and speaker cabinet, switch it off in the Global menu. This will decrease overall CPU utilization considerably.
Samples translated in milliseconds: ## Normal Res = 1024 samples = 20 ms
Hi Res = 2040 samples = 40 ms
Ultra Res = 8000 samples (max) = 170 ms (max)