I checked the CPU % difference between the “Legacy” and “Dyna-Cab” types in the FX3 Cab block, and it’s 3% whether there’s 1 or 3 slots in use. If two cab blocks are running it should only be 6%. I don’t consider that “significant”.
Whether that will scale linearly on the FM9 is unknown but it has a DSP allocated to the Cab blocks. The FM3 runs the Cab block in an FIR accelerator when the CPU % isn’t available, so it might see 3%, or it might be something higher, Fractal will eventually tell us.
I think it's quite reasonble to assume it will have a bigger cpu impact on the FM3.
Some people where expecting that these new Cabs would translate in some CPU saving (like the stuff in Line 6 ), but to me it was quiet obvious from the start when the new Cabs where first described that this is an all new "game" (meaning, superior algorithms in comparsion with the Line 6 offering).
I didn't expect any less form Fractal.Of course that comes with a cost, and that cost being more CPU usage.
For Axe III users it's meaningless given the raw power of those units, for us here on Fm3 world...not so much.
Like i said, i belive we will see these new Cabs in some capacity ported to the FM3. Maybe if you use just one cab it's feasible?
From the videos i've seen these Cabs sound as good as the best IR's out there (wich makes total sense). The real selling point (of course great sounding quality is a given) is mainly the ease of use without geting into the usual IR rabbit hole.
If it's not possible to port it...well, i have to be honest and t say it wouldn't bother me terribly (altough i have that feeeling it will be ported).
Whille i may be a minority, i actually enjoy the Fractal stock IR's on the Fm3 (i bought mine used and it came loaded with the Wellspring pack, sounds so good!). Most of the times i just match the amp with it's respective cab, cab 1 with a 57 and the second one with a 121. Done! It works like a charm 95% of the time.
I do get lost tweaking effects tough, but the thing i like most on the FM3 is just how quick and easy is to get good amp tones (i hated the amp modeling on the Helix...).
Anyway, soon we should know how this will work on the Fm3.