As a data point, I lowered the front end on my otherwise stock GL500 by about 1cm or 1/2" by sliding the tubes through the triple tree, measured using the factory engraved line in the tube. That was about as far as I wanted to go to confidently avoid the fender hitting the radiator screen at full compression. Plus the GL forks sit above the triple tree by default, so you get a little of the cool cafe look even at the standard settings.
I also have a slightly longer then normal rear shock, so the steering is a little steeper than normal from both suspension mods, but handling still fine.
I also have a slightly longer then normal rear shock, so the steering is a little steeper than normal from both suspension mods, but handling still fine.