I truly appreciate the comments and valuable information given. Unfortunately I am still trying to make my mind up at this stage but for the most part I’m leaning towards either a second-hand Canon 400 F5.6 (very reasonable priced for the most part) or the Sigma 150-600mm C. Still fresh faced and dewy eyed in terms of bird photography and as such it seems proper to forgo spending too much on a initial setup until I’m well versed in wildlife photography through practice.
I have realised that another limiting factor may very well be my 1300d which isn’t the fastest to focus under the best of circumstances and has a tiny buffer which fills extremely quickly when shooting raw. In that regard i have heard that more and more sport photographers shoot in Jpeg to conserve the buffer but in turn this limits the amount of post processing one may do. Do you guys shoot raw or Jpeg for wildlife photography?