I've got a bone stock 2008 38ZR. Staggered 525s, 1.50 ratio XRs on ITS transoms. The boat came with 34 Maximus props (I believe in the 15-1/4" diameter) as well as a set of 5 blade 33 Herings from the old owner.... I found them to be a touch large to swing and was actually struggling to come on plane when giving it any sort of power (whether due to being wore out or some prior work, they would blow out hard and not want to bite. And yes, before it is said, I do know that the blowout on staggered setups is normal as I've ran many over the years, but this setup was excessive.) That being said, I've since swapped to 32P 15-5/8" diameter Maximus and the boat seemed to like them. The only complaint I have with them is that in good water, the boat is laying pretty decently into the limiters with this setup so some more tweaking will be needed from there.

Responding to many thank you yes its an ITS drive 1.5 525 boat I did purchase a set of 31 6 blade herrings gave me a little more rpm liked the ride a little better. seems closer. Im not a b Blade fan no thanks. 34 maximus was I believe the prop It probably came with. My GPS messed up this weekend so I didn't get a good number on it I can tell you it only ran 75 before seems pitiful.

Also have a 38Zr experiencing the same issues you are. I have 525s and xr/its with 32p 5 blades. I feel like and have heard from several other owners that this should be a mid 80 mph boat and im not seeing it, 77-78 tops. From what others are saying maybe I should look into the 30P maximus props. Love the boat, just feel like it should get out a little easier and have a little more up top.
-Steve