I was just trying to figure it out in my mine.  So "once again" I was trying to figure it out.
What shocks are you running?  Those are your first limiting factors.  Once you have long enof shocks to where your spring are loose then your springs are your limiting factor.
But,
I have a set of Ford F-150 4x4 shocks on mine.  Calimni 3" springs set to where their loose and I don't think I'd want any more drop.  I/we have a slip yoke, and any more drop and I'd be worried about the drive shaft coming out to far. ÂÂ
Flexing over rock and such would not be a problem, but hitting a jump at 20-30 mph and getting a little air, the whole rear end cycles down and
Also, I remember Mike stating once that at one time he had too much articulation in the rear for the front IFS.  It was unstable.
All good points, and reasons I'm keeping all the stock stuff around. Just trying something a little different. If it works, great! If it f***s up, just bolt everything back in the stock location.
W/ a 2" spacer, I've already maxed my rear end. If I got the XJ coils to work how I liked it, I would have had a 28" uncompressed shock maxed out.
Bent a sammi rear end w/ coils? Where you jumping it? and this is a tracker axle, figure they are different, since trackers come with coils stock.