softwoods have a Tc value of 0.14 ish...
quilted insulation has a TC value in the region of 0.039
therefore the floorboards equate to about 1/4....
so if you need 10" of insulation youd need 40" of floorboards to equate to this...
so in reality it equates to about 1/4 inch quilted insulation....
if you want to increase your attic insulation you will need to either raise the attic floor level with new counter joists.... or insulate below with a new ceiling