Excellent job and qualifies for a pat on the back. ;) Perfectly safe since the breaker upstream of the #10 wire is 30 amps.
Unless you have tripping issues, you probably won't ever need to upgrade. What does the voltage inside your TH look like? Should be measured with both ACs running and also maybe at the hottest time of day if neighbors drag the voltage down in the neighborhood from them all running ACs at the same time. If you don't have one, it's always a good idea to have an EMS unit to protect ACs against low voltage.