What you actually want someone come out and do "maths" for HVAC? My installer (yes, I'm joking) just used this template.
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Personally, I think the safest approach is if a 2.5 ton unit results in your wife complaining it's too cold in the winter and too hot in the summer, then you upsize the replacement.
Joking aside, you can get a soft start (sometimes branded a Secure Start or Safe Start) installed on your AC unit to reduce the locked rotor amp current draw on "normal" copeland style compressors. This means you can use 2x Powerwalls to power an AC unit without over-loading the Powerwalls when the compressors start up. So, you don't necessarily have to get a variable speed compressor.
But
DO NOT GET A LENNOX SYSTEM. If you go Lennox, they won't let you add the soft start on the non-inverter driven compressor unit without voiding the new product warranty. Plus Lennox Industries (HQ) treat their end-purchase customers like crap unless they threaten them with legal action. Dealing with Lennox is a headache I wouldn't wish on anybody.
I agree with Wayne that the absolute best outdoor air conditioner unit will be a variable speed with an inverter driven compressor. But keep in mind these are outrageously expensive compared to a single or dual stage unit. For example, the Lennox XC25 Signature with variable speed (inverter driven) compressor was quoted to me (3 ton unit) as $5k more expensive than the Signature XC21 dual stage unit.
PS, if your area isn't very humid, for your AC system I suggest you upsize your evaporator coil slightly larger than your outdoor condenser tonnage. For example, if you put in a 3.0 ton condenser unit; get a 3.5 to 4 ton evaporator coil. This larger coil results in a higher surface area to cool the air and you'll see a bit better SEER and energy efficiency. The trade-off is that the coil will be worse at removing humidity from the air, which means your home will be more humid. I'm in NorCal so that's not an issue (hence why the state is always on fire and our electricity is always being shut down). I also don't know if this evaporator step-up approach works on heat pump systems.