I would really run a full complement of Wastelands atm, as it is very good versus GAT. Maybe some of the following ideas may help you:
Playing Leyline maindeck would really help the Ichorid and Flash matchups. Vs Ichorid, game 1 it is an autowin. The other games, you could even side in some Serum Powders. With the help of the Spheres and Wastes you should be able to protect it from the Enchantment-destruction. Vs Flash it helps you slow down the game to try and achieve a harder lock.
I think one of the most interesting cards for Stax atm is Jesters Cap. Vs Flash its like a very fast win-condition. Combined with Leylines and the usual Stax-Tempo-cards it should be fast enough to be relevant. It's also very powerful at fighting GAT. You could play two Maze of Ith maindeck, two sided and play a gameplan of "keep one Beater in check, Cap the other four".
I hope that helped you in some way

edit:
Here's an interesting example list I want to show for reference. It's built around these ideas, maybe you want to try out this version, just for fun. The proxylimit may be a little problematic, though...
//Lands 25
4 Mishras Workshop
2 Ancient Tomb
4 Wasteland
1 Strip Mine
3 Barbarian Ring
4 Mountain
4 Bazaar of Baghdad
2 Maze of Ith
1 Tolarian Academy
//Creatures 7
4 Goblin Welder
1 Triskelion
1 Sundering Titan
1 Duplicant
//Spells 28
5 Moxen
1 Sol Ring
1 Black Lotus
1 Mana Vault
1 Mana Crypt
1 Wheel of Fortune
1 Memory Jar
1 Trinisphere
4 Jesters Cap
4 Leyline of the Void
4 Sphere of Resistance
4 Crucible of Worlds
//Sideboard
4 Pyroclasm
4 Serum Powder
2 Maze of Ith
5 ??? (Thorn of Amethyst looks interesting, maybe even Main...)
Appletree