20k is more than I ever got out of the rears of any V6 Omega I've ever owned. As Al says, the TC gives them a good thumping - look in the mirror whilst playing, and you can see the dust fly off them, esp on the MFL non vented, as you can overheat the pads on TC if being a complete womble - I did this once to see how it would react, and did about quarter of a mile fighting the TC. Utterly wrecked the pads.
I guess TC is the reason they fitted vented, as even in fast road use, the non vented were more than up for the job if properly maintained.
Also, as stated by Al, genuine factory OE ones easily available on the gay of E for a tenner. Wrong fitting kit for a 2.6/3.2, but the pads are identical.