Gestalt Sneak Attack

[Fax Celestis]

The problem with Gestalt is that if both sides give the same feature, you only take it once. A gestalt Ninja//Spellthief does not have 1 level of Ninja and 1 level of Spellthief, he has 1 level of Ninja-Spellthief.

Now, if you take a level of, say, Fighter//Rogue at 1st level, then take a level of Ninja/Rogue, then continue levels of Ninja/Rogue, you'll be getting Sneak Attack or Sudden Strike +1d6 at every level, because the levels you get sneak attack in rogue are the levels you don't get sudden strike, and vice versa.

Except you've missed the bit where it says that if you have two classes that share an ability, you gain it at the faster rate.

However, Sudden Strike != Skirmish != Sneak Attack, so they'd stack.