I don't wanna rain on everyone's parade here, but personally I tried the magic carpet thing and it really didn't work for me.
Skated 8.5 trucks for years, usually on 8.5 boards. Made the switch last year to 8.25/8.38 and kept the same trucks and it was great (Venture 5.8s standard and titanium hanger with forged plates). Decided to try some 5.2 titaniums on an 8.25, padded with as many washers as I could too.
They turned a lot sharper and were much lighter, maybe flip tricks had slightly better leverage on them too, wasn't anything that made a big difference. But I definitely found myself falling off the board easier when not landing perfectly or leaning too much one way or the other when settings up for certain tricks.
Grinds on round rails and chunky concrete ledges were also a lot more difficult. Pretty much fine/the same on nice skatepark ledges but just could not find myself getting a secure enough lock in or cross pinch on sketchier rail tricks and it was much easier to miss or slip out on rounded off street ledges.
Maybe 5.6 would be okay, but I've got two more sets of 5.8 on ice so I probably won't find out for a long time.