Sounds like you may have had a whole-home energy audit done already -- including a blower door test? If not, I'd highly recommend it; I paid ~$500 for one a few years back which included thermal imaging, blower door tests, airflow measurements & calcs, current/draw measurements for all energy-consuming devices, thermal load calcs, etc. You may find better pricing even -- ours included a detached structure/office, and house is relatively large, multiple HVAC units/solar/pool/servers/etc...
In my case, I didn't end up with any super directly-actionable insights -- but it was still very well worth the money IMO. Even just to confirm that we weren't losing/"leaking" energy egregiously. The reality was, our household simply uses a lot of energy - hah.
I mention this all because, at the time, we were just about to replace our HVAC units & we had just installed solar + storage.
I'm located in Las Vegas -- summers are HOT (!) -- but our units (2x 5-ton Bosch heat pumps) can near-trivially keep us at 70F (or cooler), even on the hottest of days. I try to "push" the thermostats up a bit (we leverage a ToU energy plan), but there are days when the battle isn't worth having & the wife needs it at 69F -- and, even on the hottest Vegas days, we're able to hit it (can be expensive to do so, depending on time of day -- but is totally doable).
Edit to add -- Oversizing a system can very easily lead to issues; short-cycling, humidity control, etc. The ideal system will run nearly non-stop on "design" temperature days.
See if you can find any highly-rated Bosch installers locally; they'd likely be willing to "oversize" a system since the Bosch units are "variable capacity" (inverter-driven), which means you're less susceptible to hitting some of the common issues/concerns when oversizing traditional systems. Alternatively, the high-end variable-speed options from major brands are generally well-regarded though they can be extremely expensive (the price segmentation, and resultant value propositions, are bordering on dubious IMO).
Thanks for the Bosch recommendation. Your system is much larger than ours, but you likely have a lot more square footage (we are ~2100 sq ft). I don’t recall the exact number, but I think we are 2.5 or 3.5 ton.
Our system is old enough that it’s just time to replace. It’s the one the builder installed 14 or 15 years ago and it’s fairly low end.
What you’ve accomplished in your home is exactly what my installer tells me they can’t do. He told me no matter how large of a system I buy, the system will never be able to pul the indoor temperature down more than about 20F (internet searches for “max ac cooling” seem to back that up). He says a bigger system will get me down to the 20F floor faster, but that’s it.
I don’t believe it though because of stories like yours and because commercial spaces around here are very cold on hot days.
I'd probably suggest checking out Reddit (r/hvac for pros, and r/hvacadvice for homeowners) -- you'll generally get really good advice, often from professionals, if you provide good inputs/context.
If you have 2+ floors, you probably need (or have) zones, and it may be worth paying a professional to engineer a solution that meet your requirements. I recall finding some small businesses online that do exactly this for a nominal fee (<$500 IIRC).
You might also consider looking for residential HVAC companies that also do commercial refrigeration; the conceptual physics for commercial refrigeration aren't much different from residential HVAC, just specialized refrigerants & components that are tailored to those use-cases (ie labs often require extra-cold freezers, etc).
FWIW, my gut is you'd be happy with most variable-speed offerings, if sized appropriately. Low humidity here makes it easier, but I'm sure you can do what you want, but it may not be cheap.
In my case, I didn't end up with any super directly-actionable insights -- but it was still very well worth the money IMO. Even just to confirm that we weren't losing/"leaking" energy egregiously. The reality was, our household simply uses a lot of energy - hah.
I mention this all because, at the time, we were just about to replace our HVAC units & we had just installed solar + storage.
I'm located in Las Vegas -- summers are HOT (!) -- but our units (2x 5-ton Bosch heat pumps) can near-trivially keep us at 70F (or cooler), even on the hottest of days. I try to "push" the thermostats up a bit (we leverage a ToU energy plan), but there are days when the battle isn't worth having & the wife needs it at 69F -- and, even on the hottest Vegas days, we're able to hit it (can be expensive to do so, depending on time of day -- but is totally doable).
Edit to add -- Oversizing a system can very easily lead to issues; short-cycling, humidity control, etc. The ideal system will run nearly non-stop on "design" temperature days. See if you can find any highly-rated Bosch installers locally; they'd likely be willing to "oversize" a system since the Bosch units are "variable capacity" (inverter-driven), which means you're less susceptible to hitting some of the common issues/concerns when oversizing traditional systems. Alternatively, the high-end variable-speed options from major brands are generally well-regarded though they can be extremely expensive (the price segmentation, and resultant value propositions, are bordering on dubious IMO).