Read the figures that bind
Freighter specifications lead with maximum payload, which is the least relevant number for most technology cargo. Crated racks, cooling plant and packaged electronics fill an aircraft's cubic capacity and pallet positions well before the payload limit becomes a factor, so comparisons should start with main deck volume, pallet position count and the usable height at those positions.
The second binding figure is the door. A load that fits inside an aircraft is only useful if it fits through the opening, and door height is the most common reason a shipment changes aircraft. The third is floor loading, a dense transformer or UPS bank can exceed permissible loading per unit area even on an aircraft with plenty of payload margin, which is resolved with shoring and load spreading rather than by choosing a bigger aircraft.
