This is an old thread, but since it has been revived, I'll relate my recent experience with my 1.0 M&P 40 compact .357 SIG conversion.
S&W used to make a .357 SIG 1.0 M&P until they didn't. Aftermarket manufacturers stepped up allowing .40 S&W M&P pistols to be converted to .357 SIG. After shooting 13,000 rounds of .40 S&W through my M&P 40 compact, last year I converted it to a .357 SIG, using a Storm Lake barrel. I have over 2,500 .357 SIG rounds through it now, with no issues. The 1.0 M&P 40 chassis appears to be stout enough to handle the .357 SIG round.
For a full version, see my long term report here:
Long-Term Report on M&P 40c, Shield 9, & Shield 45