Let me try to help.... and No questions are stupid around here!
The summer tires are useless in the winter... You will be allright in light snow with only the RWD but you have to be careful.
If you have a lot of snow in your area... then get the x... If you are less than 10-15 days a year then get the RWD and make sure you get the S package with that lol.
The X can go through like a foot of snow "that is what some members claim lol"
The 19's Can be put on the X but you have to use the same size tires... And snow tires will be expensive for the 19's (Size i mean that they have to have the same circumference so that you don't mess up the traction control and awd systems)
But you can get it with the 18's and put snow tires on those rims for winter and 19's for summer with the x....
This is a RWD G35 with summer tires and 19's in the snow..
http://www.youtube.com/watch?v...lated
This is an X in the smow
http://www.youtube.com/watch?v=PIsuWIowfeA
hope this helps!
DJ