Hey John,
How about a little lubrication basics here. Although the world seems to think
oil pressure is king, what lubricates your engine is
oil FLOW. Pressure is the measure of RESISTANCE to flow. Before the flaming begins,
oil pressure serves a purpose; as a measuring tool. Since all oils thin as they warm, and thinner oil has less resistance to flow, it is natural for oil pressure to drop as operating temperatures increase. You mentioned that the oil pressure gradually decreased. Since that is a normal condition, the pressure readings you were getting indicated normal behavior. Had you had either a sudden drop, OR a sudden significant increase (assuming no increase in engine speed, which would increase volume, which would show more pressure because the oil passages are a fixed size and increased volume means more resistance to flow) then the pressure CHANGE would be a valid indicator of a problem. Sudden drop indicates a lack of oil flow to measure, increase could indicate a restriction that could be blocking, or at best, restricting full flow. The variable there is where the obstruction is in relation to where the pressure sensor is. I'm not sure what the relavance of the oil filter comments are other than most oil filters have a relief, or bypass, valve. The purpose of that valve is to allow the oil flow to bypass a plugged filter (the filter engineers understand the principles, it's better to have dirty oil flowing than no oil flowing). While the advice to change the break-in filter is valid, due to the "assembly trash" it has collected not being left available for re-contamination, it very likely had nothing to do with the pressure changes you saw.
The numbers you observed would not be unusual for a 10w30, and yes, going to a 20w50 would give you higher pressure readings than the 10w30, but not as good of flow and very likely not as good of protection under the conditions you described. This is the good ol' USofA and "more is better" is a mantra for some, but at initial start up it should be more FLOW is better, not pressure. While inital start up is a stressful time for you, the engine is operating in a no load, relatively constant (assuming a gradual increase in RPM to the break in speed) speed condition. If no errors in assembly have occured that would cause a failure, and the cooling system is functioning, you should be fine.
Enjoy