I ran a synthetic 15w40 in my 01 for about 25k miles. That car has 252k on it now and it does use some oil, maybe a qt every 2k miles or so. I was worried it was too thick for cold starts and usually about the coldest morning here is teens to 20s. Sometimes it gets colder than that but kind of rare. Most of the time I ran it was probably mid 20's as the lowest, and during summer months. Might have been my imagination but it seemed like I got more lifter tick at cold start. The last oil change I used Castrol 0W40 and it seemed like I do not have the lifter tick for a couple of seconds unless its been sitting for a few days. Once again, might be my imagination and I may try the 15w40 synthetic again. This particular oil is rate CK and SN. With my large fleet of various vehicles I wanted to find one oil to stock.

BTW, from what I recall the temp charts show 15w40 good down to 5 degrees