High Velocity (i.e. Unico) vs. Conventional system

I'm looking for a few opinions (I know, there are LOTS of opinions here).
Over the last few years, I've been evaluating replacing an existing Carrier AC system in my home. The existing unit was built in 1987 and has been working fine, though I suspect it's days are numbered. Hence I've been comparing options.
Based on my own rough Manual J, as well as estimates of a couple contractors that have been out here, the house should have about a 4 ton unit. Currently it's running with a 5 ton unit (the previous owner always liked to supersize everything...) so I'm stuck with a system that doesn't effectively remove moisture or maintain a stable temperature. So I'm looking at making some changes.
Today I had a guy in who strongly pushed a Unico high velocity system - tear out all the existing ductwork and replace the entire system. I hadn't considered this previously because, well, it seemed like overkill. But I'm comparing all options. So that's option 1.
A second option is to replace the existing units with a nice variable speed air handler and two stage compressor, keeping the existing ductwork. That's appealing as it should be quite efficient and maintains the investment in ductwork (which the contractors have told me was quality work).
The third option is to do option 2 and add another zone. This would require some additional ductwork but the guys I've talked to said that the current ducting is set up pretty well for this addition.
Here are my specific questions: 1) I've heard that the HV systems can be noisy and inefficient. This makes intuitive sense since the HV systems will require more energy to push air around. Smaller tubes = greater resistance. Plus, higher velocity would imply higher turbulence and hence more noise, though I've heard this is offset for by lower overall CFM.
2) I've heard that HV systems can be considerably more pricey. I'm waiting on the proposal, but from what I've heard, $10-20k is in the ballpark. Is it a rule that HV systems are considerably more expensive than a modern, 15 SEER dual stage, variable speed system? Or are people comparing them to run of the mill systems? For reference, last year I had a quote of $6600 for the retrofit including a Carrier 38TDB048-3 and FV4BNB006000 (with all labor etc.) which seems like a pretty decent price.
3) While the air flow isn't optimal and I think a two zone system is warrented for maximum comfort, is there any reason why I shouldn't go for the simple upgrade, see how it feels next year, then add the second zone if necessary a few years down the line? I've lived with the current non-optimal setup for 5 summers so far and it really hasn't been such a big problem. I understand that it will cost more if I do it in two shots, but are there any other fundamental reasons why I shouldn't go this route?
Thanks for the feedback. -Ted
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snipped-for-privacy@soleburymountain.com wrote:

I would not consider the first option. I would lean towards #3, but that really depends on your particular situation. For me I think it could be a winner, but I would want to talk it over with more than one person. #2 should also be fine, if you are happy now with your system, other than the problems with oversize.
I will be interested in hearing from our professionals about zoning A/C
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snipped
I would spend some time with the system I have before dumping it. If oversized, check the fan connection for the air handler. If on high move to medium. Slowing down the air will remove more humidity. Stable temps, your a little vague about the cause. If it is 115 out side the unit is going to run more often than when it is 90. Check your insulation in the attic. I added R-19 to my home build in 1999 and dropped the bills in half. Also added R-30 to the garage which had nothing. Balance the registers, I had to close down the ones close to my return and force the air to the fartherest parts to stabilize my home. You may have to do this twice a year. Lastly consider an new vfd air handler matched to the compressor.
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Why spend 20 + g for Unico , you have good ducts, maybe insilate them. I do not know If unico can reach Seer of regular systems. Perhaps slowing fan speed or restricting air flow with a filter to remove humidity will help. You risk freezing the coil , so monitoring temp at the coil would be #1. Ive heard of a freeze stat on the coil. I have a oversized system also. I run a dehumidifier and slowed fan speed . But I will put in a VS DC furnace soon with fan speed controled at my thermostat, and a coil freeze stat and remote coil thermometer.
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Thanks for the feedback folks. The quotation came back for $17k for the Unico w/Lennox HS-29 Outoor unit. That's, um, a little out of my range.
I'm definitely going to look seriously at the other options suggested.
When you mention slowing down the fan, I'm curious as to how this is done. Aren't the "single speed" units just that? Or do they really have multi-speed A/C motors that can be run with different settings? Note that I'm a newbie at A/C but not at power electronics. I've set up variable speed drives on my machine tools, no problem. Could I simply run a VFD drive for the A/C fan in the same way? Heeding, of course, the warnings about coil freeze. Any further feedback would be appreciated.
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