Yes, CPC videoram is slower to move with the CPU, not even because of the memory layout, but it's simple 16k compared to 6k on Speccy (and 8k on C64). Speccy and C64 have tile restrictions to achieve that, like they have 16 colors, but only 2 or 4 colors per 8x8 tile, but CPC has all 16 colors (from a palette of 27) you could put wherever you want, with the disadvantage of big videoram. Hardware scrolling solves this (but not as easy to do it in pixel perfect movement as in the C64). Speccy at the same time, because of so small videoram, you can easilly recreate fast moves/copies of data in the vram using entirely the CPU and still reach 50hz. The fastest clear screen on CPC could reach around 31fps (with clever stack usage to point at end of vram, 10k max at 1VBL) and memcpy even less (can only move 4k at 1VBL) so 12.5fps probably.
CGA was funny to try on my previous DOS game jam, Skellywave. Initially I thought it would be like CPC, still 16k of vram, but I thought there would be double or quad buffering like CPC, but Nope. You just don't have more than one page on hardware unless you set up a blockier 320x100 or some other weird text mode based 80x50 that looks like blocky pixel res. For targetting 8086 that was already very slow to draw things in a backbuffer and copy the whole thing. Maybe I was getting 10-15fps on the old hardware, I don't recall. So, I only renderered and erased the sprites in vram, which normally would produce horrible flicker, but I had a strategy where I sorted sprites from top to bottom, to later erase/draw timed racing faster than the screen refresh so that it never flickers if your CPU sprite rendering/erasing code is faster overall.
About 286? Depends. With a fast ISA gfx card like Tseng Et4000 it's nicer but still bottleneck. 64k of vram with 256 colors, I can get 80-95fps clearing the screen the fastest way, but copying a backbuffer will drop to half, so under 1VBL. Then you can set up mode-x resolution and hardware scroll, I've seen really smooth 2d games running on 286 or 386 this way. Now if you let the 286 or 386 do things in CGA mode on a VGA card, the original memcpy of whole framebuffer is way way faster and I didn't even to do the tricky sorted sprites trick. But I was targetting 8088/8086 so..
I saw a game called Xevious on the CPC the other day, it was really smooth, I was impressed. I'm curious about what the average fps of the Spec games were, I'm assuming around 25 with the very optimised ones getting to 50 maybe depending on the graphics. But then some aren't scrolling per pixel and different parts are at different rates I think so it's hard to get a straight answer. But I saw a conversion 'Nothing' on the spec by some Russian guy that really looks close to a modern indie game in performance, though I guess maybe it's 25fps in reality.
So if available, the double buffer would generally be used to avoid 'racing the beam' to stop flicker? That's one thing I'm concerned about on the 48k spec, if it can't do double buffer and there's all that trouble. I'm not sure if it can't at all, I just read that somewhere.
That is the skeleton in the maze game, right, I saw that and it got me thinking about spectrum versus early DOS because I thought it was running good and I was trying to remember how the games on my family 286 as a kid were, like Alley Cat and so on.