You miss the point, big deal a 486 33mhz requiring game requires an 040 25mhz Amiga shocker.
The benchmarks show a 50% speed improvement. So if you wrote any game engine and it managed 13-15fps on A1200 sans Akiko you can make it run 22fps for free on Akiko. The issue is 95% of Amiga games had sloppy n00b coding.
I think it's you that has rather missed the point. The 50% it gave for an 020 won't scale upwards linearly with faster systems. Akiko gave a 50% speed increase on slow systems where the time it takes to do C2P per frame is comparable to the time it takes to do everything else, that is to say, systems which are too slow to run the game at all. Going from 3FPS to 5FPS doesn't at all imply a 15FPS game will go to 22FPS.
For an engine of a given complexity, as the CPU gets faster, the portion time it takes to do C2P on the CPU becomes less and less of the overall time of execution time until you hit the magical copyspeed bottleneck. At that point, performing C2P takes no more processor time than simply copying data from Fast RAM to Chip RAM.
Some fast 030 C2P routines are already approaching copyspeed, once you start using 040, they get there. On these systems, using an Akiko would likely result in an even slower FPS count than a copyspeed software C2P routine. The reason for that is the way Akiko works. You have to write your chunky data to it, then read back the planar result then write that to Chip RAM all using the CPU. All that copying back and forth takes longer than simply reading the source data from Fast RAM, transforming it then writing it to Chip RAM.
At copyspeed for AGA, even an infinitely fast CPU/Fast RAM combination (where the Chip RAM write speed of ~7MB/s becomes the only rate limiting factor) would be limited to around 90fps at 320x256 for 256 colours.
Doom uses a fairly simple (and efficient) 2D BSP and optimised column and span texturing routines for walls and floors and a sprite routine for objects, each of which has been pretty well-tuned. For more complex game engines, the time taken to render the frame becomes dominant and so C2P time becomes even less important. Take Quake for example. Here you have a full 3D BSP and a much more general-case textured/shaded/depth-buffered polygon rendering system. All much more CPU work than Doom. On 68K, eliminating the C2P all together (i.e. using an RTG card) only gives a comparatively small increase in fps over AGA. For 603/604 PPC systems, you see a bigger improvement because they are able to render the frame significantly faster than the 040/060 can and the whole argument about time spent rendering versus time spent C2P/copying becomes relevant again.
