300mm vs 400mm

So I want to go to a 400mm lens for my wildlife photos. Most of my big game shots are 100 - 150 yds. for the most part. Currently I am shooting a Sigma 75-300

Does anyone have any comparison photos taken with a 300mm vs. 400mm at say 100 yds???? Just for comparison sake? I want to see the difference (how much closer an animal would appear) before I buy.

Specifically, I am looking at the Tamron 200 - 400 5.6 lens. I found one less than 300.00 has only been used twice.

Thanks in advance.

http://imaging.nikon.c​om/lineup/lens/simulat​or/
Nikon's DX is x1.5 rather than Canon's x1.6, but it should give you a good feel for what's what.