you'll learn a lot more by 90kg not going up that you will by avoiding finding out if its going up or not.
positive failure is no big deal. i wouldn't build my life around it but occasional overreaching is how you find out where you really are. knowing where you actually are is valuable information. You'll know where and when to reset, back off, add volume, etc.
take a run at 90 with a competent spotter and give it a shot, use whatever tools yuou have. the right music, psych up, no psych up, rest a day before..whatever then take a shot. it either works or it doesn't..
When it works congratualte yourself and move on.
If it doesn't then thats what back off sets are for.