What's the best horsepower calculator you can get for the wrx?

I know they aren't all completely accurate but I think having one for the purposes of seeing how the car responds to changes in boost, temperature, modifications, passengers, and stuff like that would be really beneficial. Even though they're not accurate compared to other test methods, they are accurate against themselves for comparison purposes right? A good way to tune anything that you can.

Features I'm looking for would be 0-60, 1/4mile, horsepower, g-force, etc. I've never used one but seen one used, so I don't really know what other options they might have.

I'd want this mostly to see the effects of modifications and to help me to tune my AVC-R.