@John

It's a good point the sigma is a whopper at 3 kg. I see the differences in weight and aperture in the 70-200 + 1.4 and 120-300 can put them in different leagues. However it is their similarity in price and versatility that make them comparable. A canon 300 2.8 IS is about triple the sigma and doesn't have that versatile zoom. What it does have is arguably the best IQ money can buy which as a student is almost unachievable. I was not aware the 300 2.8 came in non IS but I'll look that up thanks for suggesting to see its price difference, though at 300mm IS is very handy. The 300 f4 IS is more in my price range which as jwr noted the sigma compares well too.
As you can see from my kit I am no stranger to primes, in fact I really want to shoot solely prime due to their IQ but after a few guest speakers at my uni spoke about shooting wildlife you can't discount the versatility of a zoom telephoto, whethe it be a canon 100-400, 70-300, 70-200 + 1.4 or a sigma 120-300.
In saying all this John im sure a 70-200 and a 120-300 could be apart of the same kit as they are different enough to not be on top of each other. Or indeed a 70-200 and a 300 prime. Thanks for your input it's got me thinking again...