Greetings,
A 530/480 combination loses the crossfill ability of a 530/430,
530/530, or 480/480 combo. You'll have to learn both units instead of
one unit. Other than that, you'll get the best and worst of Garmin in
one panel.

MX20 versus the EX5000 is no comparison. The Avidyne units talks to
more interfaces, is far more intuitive, and has a larger display. If
you meant the EX500, it too knocks the MX20 out of the air. My ideal
panel is dual 430s with an EX500(0), followed by the G1000.

As for the 430 versus the 480......

I never could find the copy of my old comparison, so here is a new one.
I am a Master CFI and an expert (per a bunch of folks including
Garmin) on the 530, 430, 480, G1000, and a bunch of other units. My
specialty is training these gee-whiz boxes. I can take someone who has
never used a computer before and have them successfully completing a
GPS approach by the third lesson.

Ok, 430 versus the 480:
480:
Has 13 fixed buttons and 9 changeable buttons. Depending on the mode
of the unit, the functions of those 9 buttons change. Of those buttons,
3 are dedicated to COMM/NAV/Transponder, leaving 10 fixed and 9
changeable to the GPS.
Slightly larger screen than the 430.
Has a discontinuity 'feature' making the unit think the pilot bought
this GPS to do anything BUT go GPS Direct.
Requires expanding the flight plan, making the change, then executing
any change made.
Has Airways. Big whoop. I almost never fly them, and when I do, I put
in two waypoints that define the route, either intersections or VORs,
and I have the airway.
Has WAAS. So it is down to 7 feet and not 14.
Allows for precision GPS Approaches. Cool. The 430 will have those by
the end of the year. Neither allow the autopilot to follow the
glideslope until the autopilot manufacturers catch up.
Doesn't require hitting SUSP while going missed approach. On the other
hand it always assumes you are going missed approach.
Has a HSI screen. Good for backup, but I use the external CDIs more
often.
Default go-directly-to-start button is MAP.
Multiple ways to do something, but only certain ways are available
depending on what page or mode the unit is in.
Frequency changes require stopping whatever GPS input was being made to
make the frequency change.
Four customizable map pages that require a lot of tweaking to be
usable.
Overlays include traffic. If you want more, buy an MX20.
Big Knob, Little Knob, Cursor On, Cursor Off, Press the button, what
mode, Execute the change lets you master this unit.


430:
Has 17 fixed buttons. They work the same way every time. Of those 17, 5
are dedicated to the COMM/VOR radio, leaving 12 for the GPS.
Slightly smaller screen than the 480.
Unit assumes you will go GPS direct when no other course method is
available.
If you change something in the active flight plan, you make the change.
Done.
Requires hitting SUSP while navigating on the missed approach, until
the WAAS upgrade.
Default go-directly-to-start button is CLR, hold for 3 seconds.
In an emergency, pilots have less buttons to hit to get the unit to
change its navigation than the 480. And that navigation change does not
dump the original flight plan.
Faster to learn and use. Pilots as a whole seem to catch on faster with
the 430, and use more of its features as compared to those I've trained
on their CNX80/480s.
While there are multiple ways to do something, those ways are
consistent no matter what mode the unit is in.
You can actively work the GPS and the COMM at the same time. The
co-pilot can put in the new course while the pilot puts in the new
frequency. Or you can be in the middle of a change to the GPS course,
stop, dial in the new frequency, and continue exactly where you left
off in the GPS.
One Map Page, highly customizable.
Overlays include traffic, weather, Stormscope, and so on.
Big Knob, Little Knob, Cursor On, Cursor Off lets you master this unit.

Overall, software version 2 was a big help to the CNX80/480. It can do
a couple of things the 430 currently can not do, but not for long. It
requires more button pressing and has a steeper learning curve than the
430. Software version 2 was slapping a bandage on a human factors
nightmare (no offense to my friends in Salem). I'm hoping Version 3
will make even more improvements.

Faced with deciding between the two, I recommend the 430 and save the
2K for the WAAS upgrade later this year.

But don't take my word for it. Download both simulators, get the
manuals, and start playing with the boxes. You can also get a copy of
my Inflight Quickref Guide (www.slantgolf.com), the 'Cliff's Notes' to
these units, and use the simulators or head into your local avionics
shop with the units on display. While the manufacturers manuals are
okay, mine just simply give you the button presses and knob twists to
do something. Either way, they allow you to find out for yourself which
unit is easier for YOU to use.

This is most important. Which unit is easier for you, the one that has
to use these? Your flight instructor probably knows one, maybe two, and
as their own preference they usually choose the one they learned first.


Do you need airways which require plugging in the starting point and
the exit point? Or can you plug in the starting point, the course
changes, and the exit point once, save the flight plan, and not have to
plug in the course changes again?

Do you happen to live at an airport with an LPV approach that is
actually to lower mins than the other approaches to the airport? Will
you actually fly down that low or are your personal mins much higher?
(BTW, we have an LPV approach available to us, about an hour away. Mins
are twice as high as the ILS and slightly higher than the GPS LNAV
approach.)

Do you want to deal with the "Microsoft"-like 'are you sure you really
want to go GPS direct with your GPS unit?' 'Ok, I'll let you go Direct,
but if you don't save your changes, I won't do it and won't tell you
why.'

It's your panel. Choose wisely.

Fly SAFE!
Jedi Nein