I seem to remember another big manufacturer trying variable speed compressors, and them failing miserably.
Put in a tried and true system, and when you go to replace that system put in the super system.
If it ends up being that the greenspeed IS awesome, then great. Good for them. You missed out on a little bit better comfort, and a slight amount of energy savings.
If it ends up with greenspeed being a complete flop, then you've saved yourself years of headache, and more money than the system could have possibly saved you.
Honestly, I'm still not sold on some manufacturers modulating furnaces, and they've been out for years.
I think you'll be more comfortable dumping the money from the greenspeed upgrade, into Ultra-Aire equipment.