I can't speak for the HSM version of the sigma lens, but I have an origonal APO 70-200 F2.8 EX (Non DG version)
While I can share some people's issues on quality (my first one the lens hood went on at 30degrees off level - OOPS!
) the optical quality and build quality of my second lens, now 6 years old, is exceptional.
I use mine a ton wide open, and for me, to be limited to F4 now would be a shame.
In addition, I use it with 1.4 x and 2 X sigma TCs and it really shines as a 100-280 mm F4 or 140-400mm F5.6 zoom. Again with the TCs I use it wide open. Here the reach plus speed is something that I won't easily trade for the 60-250F4 lens.