What is your location?...this is an AC only var speed condenser system?....what exactly are you looking for?....Comfort, efficiency?...you have deep pockets?

IMO

I'm in Oklahoma City. Replacing AC and gas furnace. Looking for comfort, bells and whistles, I suppose. Wouldn't say deep pockets necessarily, but I just blew 5 grand on a coffee machine and mama gets whatever kind of AC she wants.

Slow speeds on a variable AC system mostly effect speed of the compressor. The indoor fan is modulated too, but these both work hand in hand.

Typically most HVAC brands limit the compressor on these to 5 speeds, some may be fully variable really depends on the controls that the manufacture employs to operate them. As an example: a 5 ton inverter at speed one would be running at 1 ton capacity. Each step up provides additional 1 ton capacity. The system is only going to deliver the amount of cooling needed to match demand as close as possible or load of the structure. I've heard fully variable systems run as low as 10% capacity at slowest speed on a 5 ton machine this would amount to 6,000 BTU or 1/2 ton. I don't know that you would notice a difference or much of one from a full variable or 5 speed. Because they are always searching / modulating to match the load of the structure.

Me personally, I wouldn't be too concerned with slower speeds. These systems (inverter driven) are more or less 'load matching' systems. In that regard they are almost always running. If the slower speed isn't capable to match the load the system will speed up / or in the case of over loading - slow down.

My real concern is with blower speeds at say 30% and whether I get good airflow at those lower speeds to the furthest supplies. I know where the supplies are located but don't know how the supply ducts are sized/located in the slab. Is it a safe assumption that a balanced supply at 4 Ton/100% blower will be balanced at 1 Ton/25% blower?

I'm confident in the system's ability to match the load, just want to make sure the supply is spread throughout the house, not just parts of it.

I know that the blowers run at reduced speeds but those speeds vary for various amounts of time. If the AC condenser is running at 1st step in the case of a 4 ton unit this would amount to around 9600 BTU.

That amount of cooling is based on work the compressor is doing not the blower. Just moving air will not increase the 'real' amount of cooling.

Usually blower speeds are timed at various speeds when the system turns on, but inverter systems operate as I said before by 'load matching'. So the air flow you are worried about is not really a problem, because the system is almost always running, most often at slower speeds.

The leap to inverter from what you have now (probably single speed) is a huge leap in terms of performance and comfort. I believe your biggest problem is if you ever move from this property to a home with single speed AC again being able to live like that again.

This is assuming there are no installation hiccups.

Inverter type systems are nice but very expensive. I think you will be happy with a variable speed gas furnace paired with a 2-stage AC condenser.

Very expensive is right. Thanks for the feedback guys.

Inverter systems aren't for everyone. Just like BMW's, Corvettes, Ferrari's etc.

They are for people who have everything already and want to be comfortable with all the comfort bells and whistles these systems provide.

An Inverter system only makes sense if you are planning to own the home for a long time (Typically 15 years or more). Otherwise you'll never recoup the expense / and enjoyment will be short served.

One tidbit that might be of use is that if the larger inverter-driven compressors are like my mini split compressors, there is very little start up surge. That makes them relatively easy to match to a relatively small backup genset. I'd expect 110% or less than the constant full power.