My S9+ has the Exynos 9810 chipset. As I said, you need to tweak the crap out of the device, Samsung completely messed up there. What I did:
1. root
2. installed GLTools
3. set fake cpu profile 1 cpu core (thus locking Magic Dosbox to the first Mongoose core, running at 2.7 GHz)
4. disabled power saving
Still, the results are very inconsistent. The cpu governor keeps downclocking the cpu even at moderate temperatures (<60°C), so my results are usually between 550-600.
Performance governor is also completely broken on Exynos. It's only available in certain custom kernels, and it's highly unstable, too.