Gore-Tex does not lose it's waterproofness.

All Gore-Tex articles have a coating of DWR repellant on the outer shell. This repellant causes the water to bead. Without it your outer membrane will get soaked and heavy with water. It will not, however, leak. The sogginess will make it difficult for vapor to escape and it will create a micro-climate next to your skin that is humid and chilly....also known as clammy.

I think for biking in a downpour there is nothing better than a good gore-tex fabric unless you are comfy getting wet and going without. Most are not.