arkie6 has a valid point. Kansas City MO is US climate zone 4A. With 5.5" of ocSPF you'd have about R20, which meets
IRC 2012 code min for walls, but is well shy of the R49 specified for attics/roofs.
MO state wide building codes regarding insulation is currently based on the
2009 IECC, which specifies R38 minimum for attics/roofs on zone-4. Assuming you have fully 6" in the attic you're probably looking at R22.
Just from an up-front cost point of view it probably would have been cost effective to to with smaller geo and higher-than-code-min performance on the building envelope, let alone a sub-code building. A 90 KBTU/hr heating load for a 4500' house is 20 BTU/ft
2, which is about 2x the typical heat load ratio of a code min house half that size, and significantly higher than the heat load of my way sub-code 1920s antique, which comes in under 15 BTU/ft
2. Bigger houses usually have even lower BTU/ft
2 ratios.
Some building envelope issues can be cost-effectively rectified as a retrofit, but many are not. But getting the geo to work properly would be the first priority, if that's really the root of it. The cooling load from the roof can sometimes be disproportionatly high when you have only ~R20 up there, and it may be worth treating that to more insulation sooner than later, provided it's possible without gutting the ceilings or something.
If the system has any ducts/air handlers outside of the insulation, that too can be an issue increasing load, decreasing system efficiency.