Efficiency of PSU loose ?

Hi there,

I am using Corisair CX400 PSU and its 80 Plus standard.

1. Does the efficiency decrease over time , if yes by how much?

2. Capacitor aging and relation to its efficiency ?

3. If i overclock my proccy and gpu, how does it affect the life of PSU components even if the total usage is below rated wattage ?
e.g. Total Computer suchs 260W ( overclocked and 100% full load) and PSU supports upto 350 W.

4. Does the PSU still gets under pressure ?

Thanks for replying the answers.