A connection between the simulated universe's speed of light and its host CPU's clock speed would imply real-time simulation. I see no reason why that would necessarily be the case for a simulated universe; most research-grade physics simulations humans run today aren't real-time. (They would be real-time or faster if we had the hardware to run them that way — I imagine a sufficiently accurate physics "REPL" would help a researcher tremendously — but we make do without them.)