I would expect to see more pressure than that at high rpm - perhaps the fuel filter is getting clogged?
I don't think actual fuel consumption at higher rpm is that much different, at least under no load, but there will be more flow through the pump due to higher internal pressure causing more flow back through the return lines. Would still expect more than 0.5 psi though, although i think anything that's not negative pressure will be fine. Would have to see the actual standyne specs though to say for sure.
Personally, I think the likelihood of a mechanical pump failure is about the same as an electric, possibly higher for an electric pump due to greater complexity. The electric side is simple, yes, but still has a certain number of wires, connections, switch(s), etc that can all fail, and the pump itself is a moderately complex unit with a number of moving parts to wear/fail. Yes, the mechanical pump can theoretically fail and dump fuel into the oil, however IMHO this risk is much overrated.
I have an electric pump (generic universal inline kragen unit IIRC) installed on the frame just past the switch valve as well as the stock mechanical pump. The electric pump is only used for priming or if I fell like it would be helpful (going up very steep jeep trail for example) thus giving the best of both worlds. Yes, the electric pump likely does restrict the flow some, but it hasn't been an issue in the 10+ years & probably 150k miles I've had an idi setup this way.