I currently own a Canon 70-300mm L lens which I use mainly to photograph wildlife (am a frequent traveler to Costa Rica). Generally I have been very happy with the lens. I have an opportunity to buy a Sigma 120-400mm (Canon mount) for what seems like an excellent price: $600 and it's less than 2 years old. I don't absolutely need to have it but seems like the deal is too good to pass up and I do plan to taking more trips to Costa Rica as well as Brasil and Amazonia. So my question is: is this overkill, having both the Canon 70-300mm L AND the Sigma 120-400mm or can there be justification for owning both? Thank You.