jacking up on the plate and trimming are two different things..which are you talking about???
they are independant of each other..and serve similar AND difference purposes.
you have a tach and a way to measure speed?
even with the right trim you can jack the plate and while it will not affect your porposing, you might go so high your prop loses its bite...
you would notice it first in turns, even the motor runs good going straight...( when you are jacked to high)
once you find a good height to run on the jack where you dont blow out...
you can play with the trim once on plane and watch the tach and speed...
you will peak for speed when trimming up, but start to fall off afterwards and might even lose bite and wash out the prop...
then obviously you ahve trimmed too far..
i can pick up a few mph once up on plane at WOT, if I play with the trim up a little..
I know most guys say just go by feel, but this is where i wish i had a workable usable trim gauge...because i would juts dial it in to that number and let it settle itself. and i woulnt have to watch gauges for 30 seconds..i could watch the water or anything else...
I have not experienced porposing since I have had a boat-motor combo with trim
I experienced it previously with a manual trim motor..
so i cant offer any advice on when you notice that effect while trimming..
I have floataton pods on the back and i doubt i will ever porpose with this boat..
good luck
bob