When testing with the RX 7600XT last year, there were a few scenes from the Blender demos list where the intersection boost wasn’t enough to offset the BVH construction time. However that has mostly/entirely disappeared when switching to the RX 7800XT, probably due to the intersection boost on the RX 7800XT being higher.
A user reported that the Classroom scene from the demos page was overall slower with HIP-RT. I assume this is because the HIP-RT performance boost wasn’t enough to offset the BVH construction. I and Brian Savery could not reproduce this behavior.
There’s also the factor of the render time. If a scene takes 30 seconds to construct a BVH , and 2 seconds to render on HIP. But takes 32 seconds to construct a BVH and 1 second to render on HIP-RT, then using HIP-RT isn’t worth it. But if the user increases the sample count, resolution, and/or ray bounces, then the render time will increase, but the BVH construction time will stay the same. And at a certain point HIP-RT will become worth it.
I have created a bug report here for one of them: #117527 - HIP-RT transparent shadows rendering artifacts - blender - Blender Projects
The secret deer scene renders different on HIP-RT : #117567 - HIP-RT renders some instanced objects differently from other BVHs - blender - Blender Projects
The plants in the lone monk scene from here renders differently with HIP-RT. As far as I can tell, some of it is the same issue as the Secret Deer issue linked above. Some of it is due to differences in how each backend handles co-planar overlapping faces (This is also an issue with other GPU vendors and is not HIP-RT specific)
There is a relativity minor issue on the Monster Under The Bed scene from here. The way the monster “flesh” overlaps with one of the eyes is different between HIP-RT and all the other BVH options (Embree, BVH2, OptiX). It’s a relatively minor difference, but it’s enough to cause a “flicker” in a animation rendered across multiple GPU vendors (E.G. HIP-RT and OptiX render alternate frames, and due to subtle differences in how they render this overlapping section, this will appear as a flicking piece of geometry around the eye).
In the scene where I saw the 150% intersection performance boost, the main factor appears to be having lots of fine geometry (I had a lot of plants and pebbles and twigs scattered on the ground to fill out an environment).