Most vehicles have the oil pressure sensor located after the oil filter, so the slight pressure drop across the oil filter (along with the oil gallery length between the pump and the pressure sensor) will make the pressure at the sensor slightly lower than the pressure right at the pump outlet. What OVERKILL was seeing on the gauge would be a bit less than at the pump outlet, so if he's seeing 68 PSI at the sensor then it makes it even more likely the pump pressure relief was operating, and the relief valve being slightly overwhelmed since I'd say it was probably 2 or 3 PSI higher at the pump than at the sensor - so 68 PSI at the sensor would be around 70~72 PSI at the pump outlet.Without the exact locations of the oil pressure sensor, as well as a schematic of the oil system, it is hard to say if the relief is cracking or not. If there is significant pressure drop through the passages between the oil pressure sensor location, and the oil pressure relief valve, it may not be cracking at all.
The pressure drop through the oil filter will be much more than through the big main oil supply gallery between the pump and oil pressure sensor (if the engineers did a proper design job), as the design goal is to measure the oil pressure in the main oil supply gallery feeding the whole oiling system. With hot oil, the pressure drop across a good flowing oil filter with fully hot oil will be in the 3~5 PSI range at high RPM (pump putting out around 8~10 GPM). The graph below was test data from Purolator for a PureOne flowing hot oil with an equivalent viscosity of 5W-30 at 200F. Most good brand name oil filters will flow close to this. I think OVERKILL is running a full synthetic Fram Ultra, which flows this well or maybe even a bit better.
A more interesting test would be a cold start, and slow rev from idle to high rpm. This will give you a better indication of the relief valve characteristics.
It would be a better test if someone is comfortable about revving the engine pretty high with cold oil. The test could actually be done in neutral since the oil pressure is a function of engine RPM and not vehicle speed.