oil change oil recomendation
 

I am getting ready to change oil in my 2004 Boxster S and need advice on which oil to use.
It currently is running on Castrol 5w40 Syntec.
Since I live in Tucson, Arizona which never really has a Winter I thought that I would go to the current 10W40 version of Castrol Syntec?
I stopped by the local auto parts store and discovered that Castrol has renamed the Syntec oils and was confused as to which one I should buy?
I tried the tech info center a couple of weeks ago with this question and it seemed to be only related to parts.
So I tried sending Wayne a message from the center page and probably didn't do it correctly so I am here for some advice.

The new stuff is under the label Edge and will have a little label saying Formally Castrol Syntec. It is suppose to be better but I'll let you read about that to determine. Each time I go to get oil in the 5W40 I keep finding the original Syntec, so I'm not sure if Castrol is still clearing it's supply or will keep both labels.

I've been using 10w-40 but I've been thinking about 5w-40 or even 0w-40 in preparation for cold weather starts. Seems to me the lower weight would be better about getting oil through the chain tensioner and lash adjusters. I can't see any downside once the motor warms up since the oil would be the same viscosity when warm.