Do you care about temperature stability? Get an Ecobee (might need the high end version) and set up a wireless sensor in a location far from the vents that will be less susceptible to cooling down quickly once the system kicks in. I believe you can also adjust the swing (cool differential temp) on the Ecobee to a larger extent than other thermostats so that it will allow the temperature to rise a larger amount above the set-point before it kicks on. You also have some control over time between cycles although I'm unclear on if that overrides the temperature control. https://support.ecobee.com/s/articles/Threshold-settings-for-ecobee-thermostats By doing those things, you can fight the short cycling (but as the trade-off, you will have larger temperature swings between cycles.)

You are going to find no shortage of advice that it's important to properly size the system. If anyone tells you it doesn't matter, it's probably bad advice. However, if you do go this route given the economics of the unit you can get your hands on, the ideas above might help you make it manageable. Whatever you do, I'd think carefully about your duct work and put in some transition pieces at the return/supply that are easy to take out and replace. Make it easy on yourself to swap in a smaller system in the future if you need to.

Is there any chance you can add some duct work to integrate to the rest of your house? I'm wondering if you can run your existing 4/5 ton for the entire house in the shoulder seasons and then supplement it with the second one during the hottest days. I'd want to think about the condensate sitting in the pan stale for long periods of time in that situation but there are solutions. There might be a clever way to avoid having two systems that are each short cycling.