One parameter you guys should pay more attention to, then, is the Bulk Richardson Number. The BRN is basically CAPE/(0-6 km shear), so it indicates the balance between shear and instability (much like the EHI). Research has shown that BRNs between about 10 and 50 are the best BRNs for supercells. BRNs that are too high (above 50 or 100 even more) indicates more buoyancy than shear necessary for supercells, and BRNs that are too low (around 10 or lower) indicate that shear is much greater than buoyancy. Yesterday's severe weather was definitely the latter case. I know the SPC site plots the denominator of the BRN expression, so you can just divide the CAPE by that to determine what the BRN in that area will be.