Mr Gadgets

I perfer the XR ribbed top cap myself it has a steel tower in it and is thicker than the stardard cap. The ribs afford more surface area while adding thickness to the strength of the cap. Studded to the case it firms up the upper housing and supports the vertical shaft quite well. The cost is very reasonable for this cap, even with a stud kit. (I supply my own kit). I have not had any failures using the XR ribbed top cap.
One thing to mention is that the depth of the bearing race surface is not equal on all caps. I measure each one and shim accordingly. If you have a properly setup gear set, you can measure the difference between the two caps (new and old) and change out the difference with the proper shim/bearing race. So I dont recommend someone just buy a new cap and put it on, without checking it first.
I have also found some caps with the race surface not flat or parallel. I have not found this to be the case with the Merc cap.
Cooling is another issue. If your drive shower sprays water on the sides of the case as well as the top.. it will cool sufficently to help protect the drive. When I first installed the ribbed cap on my drive (Bravo1 XR) it would chalk up until I changed out the shower to the Halo type.
So as Eddie said there are many things to consider when choosing a top cap. We each have our preferences. I was told once that internal cap cooling can be a problem in salt water, but I have not seen that where I live..

Hope this helps add to the confusion..

Dick

Griff

The XR and XZ use the EXACT same lower and the propshafts are the same.

THLWL

Didn't know the XZ was the larger diameter also. The X and older Bravo 1 have the smaller diameter.

shawn

I have two of each, and I use the Billet top cap because it came with the boat. The XZs are actually 2 miler per hour faster than the XR with everything else the same.
I use the XZs as spares and the XRs as my main drives. The boat came with the XRs and I found a pair of XZs which I bought for spares. They come in handy boating on the Chesapeake Bay.
I doubt you can go wrong with either drive.