Well that's pretty hard to say, they are both fast engines but they have a different way of releasing the power.
The P3L Black has a lot of low end power(never seen a engine with that much torque) and lacks a bit in the high end department. So if you run on short tracks that will be a great engine
The stock Eagle is a bit more balanced in power, good mid power and a good top end. So if you run on a larger, more sweeping track i would go for the eagle.

But if you really have to stretch the budget to get the eagle, which is about 30% more expensive, then i think it's not worth it and better spend it on tyres and fuel and just practice, practice, practice.