Going by your sig, since its a 91 XJ. It would be a toss up. You have the HO 4.0 and the 23 spline AW4. If it was pre '91 i would go V-8.
I would not worry about the AW4 it is a fairly stout transmission capable of the power of the stroker. It may need to be freshened up some, but not a concern.
I know you are in the middle of race season, so is down time going to be a concern? If so, which way would get you up and going quicker. Or are you going to do this after the season?
Do you see yourself going for more HP in the future, then I would go 5.3, they are easy and cheap to get some extra ponies out of..
just some points to ponder...