heres a pic,you can't really tell the ujoints are smaller but max machine makes a forged input yoke for the xr gears that takes smaller bravo ujoints

Yup, a few hard parts and some $$ German bearings for the most part. The added cost to Merc of everything from the materials to the finish work, make those hard parts in the "XR" more expensive.

I believe the "XZ" includes the bigger U-joints.

The "X" is "XZ" upper and a standard Bravo lower. I have those. I believe "X" up (or all) have the improved clutch.

Bam has an excellent breakdown of the differences on their site if I remember right.

I'm saying about 600hp .the boat doesn't have boxes.And yes the XZ drives won't last.The XZ has a smaller prop shalf.It can be changed.

if 575,s get a 353 over 90 with xr drives i am sure if you dont beat on the boat then xz will hold 600 and if not just beef them up a bit.

XR's won't last behind 575's on a heavy boat.
They're grenades.