The PlayStation 5 Pro Game Boost feature isn't delivering the 45% improvements promised before launch likely due to memory bandwidth constraints.
Speaking during the latest episode of their weekly podcast, Digital Foundry commented on the system's features delivering, so far, only a 30%, 35% improvement in titles that did not receive a PS5 Pro Enhanced patch.
While it is still not clear if Game Boost, which is essentially a compatibility mode, offers all the features and all the performance of the system, which seems unlikely, considering the Xbox Series X, powered by AMD hardware like Sony's consoles, offers the full GPU power when running Xbox One X using a similar compatibility mode, there's a very good chance that memory bandwidth constraints are limiting the improvements.
This is similar to what happened on the PlayStation 4 Pro, as the 45% GPU upgrade over the base model was accompanied by only a 28% improvement in memory bandwidth, although the unbalance was way worse in the previous generation refresh system, which couldn't target 4K resolution in games even if the system had the shading power for it. Related Story Lego Horizon Adventures Review – A Toy Aloy TrifleThe PlayStation 5 Pro Game Boost feature being limited by memory bandwidth hypothesis is somewhat backed up by how AMD handles its GPU, as the increase in CU is parallel to an increase in memory bandwidth and memory controller improvement that allows larger cache GPUs to better handle high resolutions such as 4K.
As such, there may be situations in the future where the PS5 Pro will be able to handle 1080p at 120 FPS with ease but struggle more at higher resolutions, as the higher the resolution, the more memory bandwidth is needed.