I'm going to Alaska for 2 weeks this summer. I'm trying to decide if I should buy (or rent) a 300 f/2.8 VR. I have a 70-200VR and both the TC14 and TC17, but I'm not sure that 340mm will be long enough for some of the wildlife. Weight is the key thing keeping me from taking the 300. What are people's thoughts? Thanks in advance.