Depends on the situation.
For a Cobra Roll, when you enter it the front hits it with more speed than the back. As the front starts up the cobra, its causing the train to slow down so the back will pull less G's entering it. Through the middle of the cobra the variation wont be as large since the speed doesnt change that much.
Now as the train exits over the top, the front isnt going very fast. But as the front of the train starts down to the exit, its pulling the back of the train with it - gathering speed. So naturally the back of the train, going faster, will pull more G's upon the exit just like the Front of the train pulled more g's on the entrance.
A tip that most people dont do - B&M does not make their cobra rolls with first half equal to the last half. The second inversion of the cobra roll is always lower because of the decrease in speed.
Heres some shots:
http://www.rcdb.com/ig764.htm?picture=6
Good pictures below
http://www.rcdb.com/ig2169.htm?picture=18
http://www.rcdb.com/ig2528.htm?picture=41
Even if you dont do it B&M style, its smart because it means both sides should feel equal.