Well basically yes, not to suggest this is inevitable, but if you run high ratios like that and boost to much higher psi levels, you can stress the engine to a point where mechanical failure takes place, prior to any appreciable knock levels detected.
Much better to stick with 20% or even 25% maybe, and work from there being safe, until we get some more data on how far you can safely go.
Anyhow, if your basically stock, 40% isn't going to give you any more than 20% is, and it will limit your power potential.
The real power is in the 98 (more energy, less volume), with the Ethanol supplying the enhancing benefits I spoke about earlier.