i've researched both of these pickups and i would like to know if these pickups sound any different from one another when the tw is in humbucking mode
I bet IbanezPsycho would know. My guess is yes.
No, Identical. It is sweet as a single as well. Well worth the extra money IMO
the 81tw is exactly the same as the 81 in humbucking mode, just like the 89 is identical to the 85. Keep in mind that it's not a pop-in replacement, and it uses a 7 pin quikconnect rather than the standard 3 pin.