You want to be careful with very light projectile loads unless you have tested them already with the firearm in question. There may not be enough energy created with a lightly loaded 90 or 100 grain projectile to cycle the slide reliably. You may well find yourself having to move up the charge scale to the point where you might have better off to use a heavier more common projectile anyway, or use a drastically lighter recoil spring (which may invite damage to the slide or rails). If I were you I would go with the more common 115grn projectiles and work with some different powders to see what you can get away with. If you are really stuck on getting down to 90grns, buy some 115s and drill a hole in the centre of the base until you remove enough lead to make it 90grn.
Recoil = Mass of firearm X Mass of Projectile X Velocity of Projectile - you can't beat the math.