Fire Resistance Rating of a proposed design

We are proposing to install a "fire barrier" wall that we believe will qualify for at least a 2-hour fire resistance rating.  The existing building has a partial wall in place which has 5" steel poles supporting the structure above.

It is essentially two of a 2" x 4" wood stud, 24 in. centers, wall, set back-to-back, so there are 4 layers of 5/8" Type X gypsum in total.  Studs are staggered 12", and drywall installed vertically so that all seams are supported.  The 5" poles are integrated, and the boundary sealed with fire-rated caulk.  And mineral wool insulation will fill one side.  See the drawing.

I would be interested in comments on whether this passes muster, or if not, why?  We have compared it to a design that is rated for 2 hours. UL Design U360 is posted on this database:  http://database.ul.com/cgi-bin...sistanceWizard.html#

We believe our design would have higher resistance because: 1) it incorporates 4 layers of gypsum (vs. 3), 2) uses mineral wool insulation which is essentially not combustible (vs. sprayed cellulose), and 3) those poles, if properly sealed are more resistant than 2 hours.

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