Syntec 5w40 or Mobile 1 0w40
 

This is for a 1.8T TT,

I know both of these oil meet Audi's specs, and both are on the "lower end" of synthetic oils, but both are readily available so they are convenient. Also, My TT has 110,xxx miles on it, so I dont know how much that factors into it. Also I live upstate NY so it gets pretty cold up here, occasionally hits single digits F. I do not know is a 5w or 0w would make a difference on those cold days or if its negligible. Let me know you thoughts between these two. Thanks

They both fit into the same general viscosity grade. If they choice is between those two, and price is a factor, just go with whichever is cheaper.

do you think there would be a issue in changing from syntec to mobile one depending on whats available at the time? I have to assume no, since they both meets the same standards.

nope. won't be a problem

I was thinking of going with the mobile 0w40 during winter and the castrol 5w40 during the warmer months, I drive under 10k a year so that works out pretty good. I am sure the difference wouldnt even be noted but I am obsessive about certain things. would this be a complete waste of time? do you think switching the viscosity's and brands once a year would have an affect on the engine? doubt it, but there could be something I am not considering.