Looking at a new lens for the Canon

At the moment I have a Canon USM 55-200, Tamron 70-300, and the Canon "Kit lens" 18-55.

I have had very poor results with the Tamron when photographing fast moving objects, but some very good results with the Canon 55-200.

My budget won't allow me to spunk nearly £700 on the Canon Lens I want, so I have been looking at the Sigma range.

I have been offered a Sigma 55-500 telephoto F4-6.3 lens with HSM technology for very good money But I have never had any experience with Sigma products.

Now, with the issues I had with the tamrom being a bit slow for my liking, and the Canon being fast enough due to the USM lens, I need to find out if the HSM technology lives upto the hype in the real world - as attempting to photograph a car at over 100mph is a bit difficult with a shit slow lens as you will all know

Any views on the Sigma range of Len's would be appreciated -Tiff