Yes, those two Noctua models are comparable, and both are very likely to last a long time. The P12 model is a slightly older design and hence a little less expensive, but it actually has slightly higher performance in terms of max air flow and backpressure specs. It does lack the built-on vibration-damping corner pads that the A12 model has. Those are not of huge importance, although I see that the original fan with that cooler had them. Their function is to reduce transmission of vibration into the finned heatsink, not for avoiding mechanical problems, but simply to reduce generation of noise. Since the Noctua fans all are relatively quiet, I doubt the noise differnece between the fans is a significant issue.
Noctua ships their fans with little items called Low Noise Adapters that can be inserted into the fans' power connector. When you use them with a mobo-based automatic speed control system such as the CPU_FAN header, do NOT use those items. They really are needed only if you have no other means of speed control because the fans are powered from the PSU with a fixed 12 VDC supply.
You should be aware of something. The speed of the CPU cooling fans, and thus of the internal CPU temperature, is controlled automatically by the CPU_FAN header. This control is aimed to keep the internal temperature at a target value suited to that CPU, and the fans are just manipulated to reach that target. By adding more cooling capacity, you will NOT change the actual operating temperature inside the CPU for most low-to-moderate workloads. What you will do, though, is allow those fans to run a little slower for the same temps, AND add reserve capcity. That is, at very high workloads, the fans will speed up appropriately and ensure that the CPU is well cooled even at max workload.