Do you want boring reliability or the excitement of not knowing if your unit will begin making crackling sounds, begin responding slowly to switch presses or MIDI, or stop processing sound at any second?
in my experience with Ax3, it's not that abrupt when starting to push cpu - maybe the odd ugly pop or click here and there. As the CPU gets pushed harder and harder above 80% the number of snap/crakle/pops will increase and eventually, once CPU is really strained, you'd have a complete cut off. Also, different combinations of block channels engaged can raise CPU levels - so maybe your preset sounds OK at 82% but you hit a switch that changes a compressor from a "pedal" type on chA to a "studio" type on chB n then you start getting more crackles since studio compressor requires more juice. Far better to stay below 80% (like with all computing devices really) and try to squeeze more out of it by reducing reverb quality, cab resolution etc.
