I use mostly a pair of standard lined trackpants and a pair of Rip curl waterproof ski pants over top. the only real reason for the track pants is they slide easily against the interior of the Outer Rip Curl pants and I'm damn lazy.
Get up at 3:00 am put on track pants, drive 4 hours to hill, put on exterior pants, ski like mad man all day, take off outer pants, drive home 4 hours. all that changing, freezin your twig and berries off while giving the car load beside you in the parking lot a free show is for the birds. the track pants are comfy to wear and dont get to hot like some other base layers I have worn in the past. IE fleece lined with light slightly windproof not waterproof at all exterior, fleece only pants etc...
On colder days I put on a pair of Descente cycling long pants without the protect the twig and berries padding under the track pants. again slick exterior to prevent bunching, moisture whicking to prevent that prob. and it's damn sexy to prance around in them in the parking lot should the need strike you.
I just finished a -16 C day with only the track pants no problem and have done -20 C days that way as well. I only break out the sexy pants if it's going to be below -20 C all day.
Worry more about the outer layer.