Stacking of Icon and Wep mods???

I have a Mes/Monk who recently got a green staff with half time recharge and half time fastcasting, 20% chance on both and I have a Icon with the same. Does this mean both mods are increased to a possible 40% chance?

36% and not 40%. For more info., have a read of the discussion in this thread:

http://38.99.233.252/forum/showthread.php?t=59362

Also, you can't use an offhand item while wielding a staff. You can arm up a staff and an icon, but the icon's abilities are disabled.