However, these DOS-games usually fail in sped up emulations because they make assumptions about external inputs such as the Real Time Clock.
I think the point of OP was that we can't reasonably speed up the "RTC" in a brain emulation if you want it to interact with the real world, because that would break all sorts of hardwired assumptions.
For a simple example, if you ran your brain at 4x speed then it would perceive everything in super-slow-motion. At that speed it would already have difficulties to understand when you speak to it (at the least it will have to be a very patient brain).
At higher speeds pretty much all cognitive functions would probably break down - unless you feed it recorded inputs that have been accelerated to match the brain-speed.