Markus - I expect it not to sound BAD, which is a sound you must not have experienced yet, because it makes everybody who's heard their engine do it very worried.
Also, once I found the right oil my engine is not noticibly noisier down into the teens. We all love our cars, why should we make do with excessive noise (and excessive wear / damage) at a cold-weather startup when we don't have to?
Bluesubie - Mobil 1 will be less viscous than the Castrol in any given grade because Mobil 1 uses no viscocity modifiers. But I think something about the viscocity modifiers combats the slap/knock/lifter noise in a way which isn't captured by looking at the figures. By the way, I think the middle number for the Castrol should be 63 cST.
8 - why not shelve the Mobil and use it when it gets warm? How many more nasty starts do you want to put your engine through? I dumped oil which had 1000 miles on it as soon as I began to suspect that it was at least contributing to the problem, and I'm glad I did!