I had a similar problem with the erratic oil pressure reading on my speco electric oil pressure sensor gauge. At 5000RPM the gauge got really erratic and even dropped to 0 PSI at times. However, when the car was on a Dyno with a workshop oil pressure gauge (i guess its mechanical), the oil pressure was a constant 70PSI under acceleration. I have never had the stock oil pressure light come on though.
Might be worth checking that there is no rubbish in either of the sensors, if you havent done so already.
My 5K also has an intermittant ticking noise (like a lifter). I too am running Hydraulic lifters, but have never considered it to be a severe mechanical noise. But annoys me regardless, considering its only 1400kms old.