FWIW, my original springs with roughly 140K miles on them tested at 77.8 lbs @ mounted height. The new springs from Sealed Power (VS-693) tested at 82.5 lbs., again shimmed to the mounted height spec'ed in the manual. This spring fits a lot of other applications, including the 7.3L PSD.
Remember that the amount of shims you should use is dependent on the valve recession spec... how far the valves are sunk into the head... to get the right seat pressure. You can add a little shim thickness to increase seat pressure if you want but you have to be cognizant of coil bind at full lift.
Valve springs any stiffer than needed for the boost and rpm range just soak up horsepower, decrease fuel economy and increase wear on valve train components. IMO, the VS-693 springs,and their equivalents in other brands, are more than sufficient for stock or mildly-to-moderately built IDI. Think about a PSD... runs two to three times as much boost as us and can turn a few more rpm. The vast majority of us are operating at the 3300 rpm stock redline and 10-ish psi boost, so the stock springs are more than adequate.... but if you need six, load six.
