I've read the release notes and agree that in the most recent firmware versions the Speaker Drive is much more usable and gives some good attack texture to tones, especially lead notes. It can be a bit much on heavily overdriven rhythms though.
The knob has a wide range and, while it isn't obviously intuitive, it seems most agree that it works best somewhere between 1 and 2.
I actually set mine at 1.0 as I've found the effect quite pronounced even at that setting. I tend to run my Amp blocks, typically JCM800 or SLO-100, at very high Master Volumes and I wonder if that is related to why Speaker Drive has a massive effect even at low settings. Does anyone know if the Speaker Drive algorithm takes into account the Amp Master Volume or other aspects of the amp model? Does it take into account guitar output level/right-hand technique to vary between cleaner and rougher the way the rest of the amp model does?
It may be that Speaker Drive is still a work-in-progress from Cliff. I suspect that if it were "all the way there" Cliff would probably set non-zero default values for Speaker Drive for each amp. I know that this would have to vary depending on what speaker cabinet is used, and there's no way for Amp blocks to know what Cab blocks are doing, but Cliff already defaults cabinet frequency resonance values based on the most-likely paired cab.
