RE: 1/4 or 1/2?
Not claiming to be expert, but the simplified version of the main difference is torque vs. HP. You will gain more lower end with the 2-1/4 vs. the 2-1/2. Likewise you will have more top end with the 2-1/2 vs the 2-1/4.
Like most of life, it's a compromise one way or the other. Determine what's most important to you along with any future plans you may have for the car.