If the sensor fails, your readings are wrong.
A mechanical gauge is generally pretty accurate, and does not have any sensors to fail.
Problem is you really should not be running then "inside" of your car. (Line could fail, and then your pumping hot oil into your car.... Fire or burning of occupants is a good possibility.)
I have a modified oil system, and at startup get nearly 75psi, then as the oil warms up, drops to just about 20ish. On really hot days, or when the engine is fully warmed up, it will be down about 10, but on the stock gauge, it's all just a guess I suppose. (I was hoping for 30, but that's not going to happen at hot ldle.)
I'm running 10 quarts of oil, and I use 15/50 Mobile One with a quart of Lucas Synthetic addtive in there. (Nice and thick, and sticky.)
No foaming issues.
You should be able to run 6 or 7 on a stock setup before your going to see any foaming issues. The oil in the pan is quite a bit lower than the crank/rods spinning above it. Of course when your slowing down or speeding up, or turn fast corners, the oil sloshes around and can come in contact with the rotating assemby, but only for a few moments, and that's not going to whip it up into a froth that will cause you problems. (It takes a few min of being over full to whip up enough oil "foam" to cause problems, but when that does occur, you had better turn off the motor fast or your going to lose it.)
When I first started up this engine, I had 12 quarts of oil. It was slightly too much, but even then it did not foam up or cause any other probems than being pushed out the valve cover ports and my breather vent. Also popped my dip stick out, and caused it to leak there.
New o-ring at the dip stick, and 10 quarts turns out to be perfect for my car.
I used to always run 6 quarts on my old engine. (Slightly over full on the dipstick.) Easy insurance from rod knock in my opinion.
One last thing. Ditch that 10/30 oil. Even in winter, it's too thin for the 7M engine. Especially if your engine is older.
Run 15/50 synthetic and your going to be fine. It's easy for synthetic oil to be pumped when cold, and it's going to have better film strength and viscosity when hot than your current oil. This all adds up to better pressure at the gauge, but also better lubrication at the bearings where it counts.