CHarger426, the HP ratings on the Champion site have no real useful meaning unless they are qualified on how they have calculated the the average BTU's and applied them. A 26", 3 row rad will not cool 700 HP continuous. So, the Champion numbers are based on some assumption of duty cycle and average actual power, not their actual listed numbers. How well the match your particular use is always hard to say; they never publish actual BTU ratings.
For the OP, the issue of sitting in traffic will likely be the worst case. You might get by with a 22" radiator with a very good OEM type fan and shrouding. But I see no good point in taking the chance and ending up too short on cooling capacity and having to buy twice. It is like cutting lumber: too short is hard to fix; too long is easy to fix.
