How closely do GCMS spectra typically agree to conclude a match?
I would never recommend making an assignment of identity based on Mass Spectrum alone - usually you'd want to get things like IR or NMR Spectra to further corroborate your identification but supposing that the underlying chemistry of the reaction is simple and that all you can do is mass spectroscopy you can use this to identify compounds.


  Unknown-1 is Compound B


Plausible, but the base peak of Compound B is 83, but the base peak of Unkonwn-1 is 55. Need more information, but reasonable guess.


  Unknown-2 is Compound A


Unlikely as the base peak of Compound A is 69, which is distinctly missing from the spectrum of Unknown-2. Unknown-2 also has significant peaks at 55-57 which are insignificant in Compound A's Spectrum.


  Is having the same set of M/Z fragments good enough or ought the abundance ratios also match mostly?


You would have a much stronger case if the abundance ratios also matched. Remember that the peaks are formed by the breaking up of the compound and the relative stability of each fragment. If the compound is the same and run in similar conditions, it should, in principle, break up in the same/similar way.