For required charging of absorbed glass mat, apply 14.4 volts corrected for temperature. Whatever the current ends up at is the correct amount. The current requirement suggests ("suggests"" has a specific meaning) that some minimum level of laminar plate/electrolyte stimulation is needed. When I get a chance I'll try and use some bamboo splinters and get an answer.
The 1.300 specific gravity used in mat electrolyte indicates the battery can withstand -60C temperature when fully charged. PT are you sure about the figure you expressed above regarding temperature de-rating? Is it for FLA or for 1.300 AGM?