I personally own the
IS and have owned the non
IS. Only reason for an upgrade for me was I needed it for the other things I photograph besides aviation.
The
IS has helped me with low light aviation photos. I prefer it over my 100-400 when conditions are not sunny as I find the optics on it to be far superior.
Price difference is the
IS currently is almost double the cost of the non
IS version (new). Probably could get a decent used
IS for $900 or less. With a purchase like this I would seriously recommend you try out both the
IS and non
IS versions to see for yourself what the difference between the two is and really make up your mind that way. If you have a camera shop near you you can bring your body there and they should allow you to mount it to your body and see what it is like... at least that is how it works here in the States. Been to a few of the bigger places in NY/NJ and have been able to play around in the store with the lenses when I was on the fence between two. With the
IS/nonIS set-up you really will be able to see the difference in the store.
Lastly, my opinion on the matter is you buy glass with the intent of keeping it for a very long time. SLR bodies will come and go with shutters having a limited life expectancy and technology ever evolving. However, lenses really haven't changed much. Yeah Canon has come out with some new glass and stabilizer technology, but the overall quality and sharpness has been pretty stable. I say go with the
IS version as you will most likely use it a lot.