Cycle accurate compared to what?

Even with a cycle accurate CPU you'd still have a lot of variation caused by the motherboard chipsets, DRAM speeds, cache chips and graphics cards.

Tseng ET4000 was on a completely different level than something like Cirrus Logic CL-GD510 or heaven forbid, Oak Technologies card.

If the era appropriate PCs had huge variations, what extra does cycle accuracy really bring at this point? The same PC demo could perform very differently on two 486DX2 66 MHz PCs.