The S.I.R. was the coolest rail system 1993 had to offer.
The higher rail meant to mounted optics needed lower mounts or you had to place your optics forward on the HG.
Times have changed, however the S.I.R. has not moved forward much. They are heavy, bulky, and over-priced (relative to the other offerings on the market).
My advice-
save a hundred bucks and 7oz and go with a nice comfortable Omega.