looking for a telephoto. lens

[chopsie]

Hi

i have a tamron 70-300mm lens it was bundled in with my camera when i bought it. I can get fairly good shots of my boys bodyboarding with it but this usually involves me getting wet. Anyway im looking at either the 120-400 sigma or the 170-500 sigma. I have read a few reviews and the 400mm seems to be the better lens. So i wanted to ask will i notice a big difference between the 400mm and the 70-300mm? Or would i really want to go up to the 500mm?. I want to be able to stay dry on the beach lol. Aswell as get up close at the zoo widlife parks etc.
Any help gratefully received

mick

 

[artyman]

As a general rule you can never have enough length when getting a long telephoto, the successor to the 170-500 is the Sigma 150-500 OS which is a cracking lens and offers the best bang for buck, if finances are tight then the 120-400, but I'd recommend spending a bit more for the 150-500.

100% crop from Sigma 150-500 on 7D