Sigma 70-200mm f2.8 os with 1.5x extender tube - great lens

There's a ton of comparisons online regarding the famous zoom length of 70-200mm lenses. Yes the native versions are great, but I've found my Sigma 70-200mm lens f2.8 OS (optical stabilization) works extremely well in many circumstances, even on my crop sensor Canon 60d. Because its a cropped sensor camera the actual focal length is magnified by 1.6x, so in affect we have a 120-320mm reach. Using the extender tube 1.5x it extends the reach further by 0.5, so in effect I was shooting the picture below at circa 500mm. When you add the extender tube you lose an f stop, so the maximum I could shoot at was f4. The shot below was actually taken at f7.1 at 1/500th shutter speed because the available light was so good. I was at least 150m's away from the action in this shot. I think the clarity and colours are great. My point is that Sigma lenses are a really good step up from the kit lenses most people use. Sure there are more expensive alternatives that have the brand cache, am I'm sure they are excellent too.