Man, I've been tempted to bite on a Quantarray. The prices are great, although I haven't read much positive stuff on them. But your shot looks pretty darn nice to me. I just found out that my old Sigma 300mm lens isn't compatible with my Digital Rebel, so I went at lunch and picked up a new Canon 75-300mm f/4-5.6 lens today. I just can't bite the bullet and spend the cash on the big f/2.8 lens yet!
As long as light is good, that lens will produce a lot of good shots. The 300 that was shot with was a 4-5.6 as well. If I recall, it was $120 at Ritz/Wolf.
Auto Focus is the lens (Quantary) biggest issue, SLOW! You have to use the pre-focus method to get anything (action) with it. The next step up (Sigma 70-200 2.8 DG) is a MAJOR increase in $ ($700+), but man, I love that lens.
This is the one I actually meant to post here ... I like it a little more than the first one. The same lens. Truth is, both are a little too soft for my liking.
The Canon I just picked up has the USM feature which, according to the literature, is supposed to produce more torque for faster auto focus. It's supposed to be completely quiet too, which will be nice for shooting graduation and indoor events.