I have few questions about using OAS as a measure of risk:

1. does OAS allow for comparison between bonds with and without embedded options (e.g. a callable bond against a plain vanilla one against a floating rate one)?
2. Is the OAS of plain vanilla bond equal to its Z-Spread?
3. If 'yes', building an OAS curve to compare all issuer's bonds having same seniority is a correct way to seek cheap vs. expensive bonds?
4. We know that $\frac{\Delta P}{P}\cong-\frac{D}{(1+y)}\Delta y+\frac{1}{2}C(\Delta y)^{2}$, where $D$ and $C$ are bond's Duration and Convexity, while $y$ stands for yield; if one uses Option Adjusted Duration/Convexity, is he allowed to use this second order approximation to estimate bond's price variation?
5. If you have a callable bond, is Delta the risk neutral probability the issuer will call its bond?

Thanks,

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