Just keep trying. Some games run with higher cycles tham others. At some point, you’ll notice sound crackling/skipping. That’s when you’ve reached your device’s limit.
You could also try some more sophisticated cycle settings, to be more flexible, like this:
cycles=auto 12000 105% limit 30000
This will run Dosbox at a minimum of 12000 cycles, with the “max 105%” parameter, and allow up to 30000 cycles (which your device can’t reach anyway, so it’s sort of an open-end value).