In calculating the psf, adding premiums per floor is really risky. Most people will pay more for a suite on the 18th floor vs. the 2nd, but from 4-12 or 6-13 there will almost never be a premium charged by the seller in resale - everything else (view, direction facing, etc.) being equal. The only guaranteed premium would be for a PH unit.

Also, to make sure you're comparing apples to apples-ish, make sure when comparing resale to new construction, that in the new construction you calculate the total cost. Price of the unit, plus parking (and/or locker) if the unit has it, plus all of the associated closing costs (land transfer taxes, lawyers, adjustments, etc.). Many new construction projects will neglect these when telling you the psf and these costs can easily add $150+ more to a psf bottom line.