I am very close to ordering the sigma 70-200 F2.8 for an upgrade from my nikon 55-300. I am currently using the D3100 and will probably be using it for the next 2 years. Firstly I was just wondering if the lens is still at its best although it is on a crop sensor body, eg speed and sharpness? The second question is if I need a bit more range how is the Sigma 1.4 teleconverter? Does it get very soft at the long range? And lastly this is just an add on question. The lens here in Australia goes for about $1400 but I am looking at buying it online from Digital Rev Store (http://www.digitalrev.com) which I can get it for $1200, has anyone bought from this online store and if so how was it? from the reviews that I have read it looks like that it is not a black market store and gives local warranty.
thanks in advance for the help