I think X-2 is one of the fastest because even if you get a pre-emptive strike you have to be quick in inputting your commands or the enemies act before you do. And I always turn the dressphere change sequence off.

One of the biggest flaws of the combat systems of both X-2 and XII was the magic queue, IMO. You can attack infinitely as longs are you're not targeted by the only magic spell that can be cast at a time. Granted, if there was no queue it would look a bit like XIII, but it would've been better. I can't tell you how annoying it is when you can't use Sentinel in time to block things like Megaton Press or Meteor.