"I did however discover something great in this fight. I thought it would be a good time to try out Similacrum with Imoen" ...
Uh oh! You
are playing Tactics I guess, where anything goes!
I bet Vhailor's Helm's starting to look a lot more useful now!
Your Anti-Paladin's THAC0 should be good enough by now to use any weapon, so if you see advantages in the Githyanki sword, I wouldn't be too hesitant to use it.