James is the man, plain and simple.
I will admit that Russell Allen has a more listener-friendly voice, but there is no way that he can handle a tour as extensive as Dream Theater's, especially considering the length of their shows. I've seen Symphony X six times and Dream Theater eleven times. The last time I saw Symphony X was at the Metro in Chicago when they were on tour with Devin Townsend. At the time, it was the most extensive tour they have done in the States, with something around twenty dates. They were playing 90-minute sets on that tour. Russell was hurting that night. You could tell that he wasn't used to touring this much. In contrast, the second-to-last time I saw Dream Theater was at the Riviera (Chicago again) on the Train Of Thought tour. The U.S. tour alone had nearly twice as many dates, not to mention the fact that they had just gotten off of a European tour and would be hitting Japan afterwards. In addition, their sets were twice as long as Symphony X's. James was on fire for that show, and he has been on fire since their tour with Queensryche. Credit must also be given when you consider that LaBrie suffered from ruptured vocal cords ten years ago and never gave himself ample time to recover. Another question comes to mind: will Russell sound as good live as James does when Russell reaches his age? Love him or hate him, LaBrie has an extensive range, a very unique tone, and a ton of stamina. At the very least, he must be doing something right if he has as many fans as he does. With that said, I never want to see Dream Theater at ProgPower. Mullmuzzler would be a very welcome addition, though.
Stay metal. Never rust.
Met-Al