As mentioned its how you drive and how much TQ you got... my CL65 tore thru my PS2's but it had almost 800 lb/ft of TQ.
My 997TT has 12k miles and the PS2's are almost done. I think 10-15k is fair based on driving habits and TQ.
2015 Porsche GT3 White
2014 Ferrari 458 Italia Rosso Corsa
2012 Ferrari FF Bianco Avus
2012 Audi R8 V-10 Ibis White
2012 Mercedes Benz C63 AMG Black Series Obsidian Black