Comparison of two Canon telephoto zoom lenses

buggers707

I'm looking to get a new lens, and have narrowed it down between these 2; Canon EF 70-200mm f/2.8L USM Telephoto Zoom vs. Canon EF 70-200mm f/2.8L IS II USM Telephoto Zoom. The first one is just USM for $1,500 and the second the IS II USM is $2,500. With such a price difference, I'm wondering what the real difference is, and if the second is really worth the extra money?
I occasionally take family pictures, but I'm usually taking western pictures of horsemen gathering cattle and such, or scenery.
I have the Canon T3i.
I am looking to upgrade from an old Tamron 70-300mm.

PBked

Hi there.
As you point out, the only real difference is the IS and I'm not sure that it is worth the extra price point. Optical clarity of the two is about equal. May I suggest that you also consider the EF 70-200mm f/4 USM IS? It costs much less than the f/2.8, has great optical performance and is about half the weight. The f/2.8 is an extremely heavy lens. f/4 is ideal for your shooting situations.
If you want a good, reliable review of the f/4, look up 'Ken Rockwell' on the internet.
Best regards, PBked