Are you looking to replace the AX4's or are you looking to add a 'deep day' ski?
First, in two years you'll want newer skis, you will. Don't plan on this purchase being with you two years from now, buy what makes sense now.
Second, the Katana is a really good ski but it's not an all mountain ski. I sold two pair of Katanas to two different tele skiers. Both of them are regularly featured in Backcountry magazine, one LOVES them, one brought them back after two days and switched to a more conventional ski.
If you have a very progressive/ aggressive tele style and get the ski on edge very early you might like them, if you have a more laid back style you probably won't like them at all.
Gotama is a universally well liked ski, it's extremely versatile, the 'safe choice'.
Why are you only considering Volkl?