My 14 year old and I both shoot Outbacks. My 12 year old shoots a Mustang. My nephew has my old FX. Each and every one is a great bow!
My son's best friend has a DXT and loves it. But my son says that other than for the slight weight difference (if that matters to you), he would not trade his Outback for it and he has shot both side-by-side many times.
I have two friends that "upgraded" from Outbacks to Switchbacks when they came out. Both have since sold their Switchbacks and bought Outbacks again. Why?
There is just something about the Outback... It shoots sweet, is extremely forgiving, lightweight, and rock-solid dependable. Mostly, it is just one of those bows that just, well, shoots great. Better than it should, maybe. If you own a Legacy, you know what I mean.
Overall, you simply cannot go wrong with any Mathews. Especially the Outback and DXT. I did not see any improvement worth buying on the Switchback that the Outback couldn't already do. Find what you like and pay no attention to what the speed ratings or which one is newer. Keep the one that shoots best for you. That's my philosophy.
I told the local dealer for years I would NOT buy any new bow because my FX shot so well and was so reliable. It would take an extremely impressive bow to make me upgrade.
So one day, he put his own new Outback in my hand and sent me back to the shooting range... Even with a strange bow the wrong draw length and poundage for me, I simply hit everything I shot at. NO hand shock. NO noise. Pure shooting pleasure.
It became my first new bow in over a decade. It would take another awesome improvement to make me switch. The DXT is different, but not necessarily better, or "better enough". I like things that last and that are tried-and-true.