Sigma 120-300mm f2.8 OS -- VS -- 300mm f2.8 primes!

[Overread19 7]

So I've been prompted by a few opinions I've read over the last few days to have another peek at the new sigma 120-300mm f2.8 OS lens; mostly by the opinions of a few who have tried them against lenses like the canon 300mm f2.8 IS L MII both bare and with up to 2*TCs and then ended up walking away with the zoom over the prime (when cost was not a factor - ie they could afford either).

So I've been looking around and would be eager to hear of any here who have had the chance to use and/or compare the lenses. The sigma retails new at under half the price of the canon and if its quality is generally "just as good" it makes a strong argument for considering that lens as a viable option (freeing up future funds for other gear or even jumping for one of the really big primes!).

Thus far the only generally agreed differences I can find are:
Sigma is softer in the corners
Sigma lacks the focus limiter switches and is a bit slower in AF - though I've yet to really determine how big this difference between the two actually is.

Optical quality is a bit iffy in that many are either getting "bad copies" of the sigma or are hitting technique limits when they post early reviews and opinion with a long; heavy lens and not using the right shutter speed/viable support.



So any here got any more to add or reviews they've found that might be more insightful?

Ps - I know the best answer is to try them both out myself, but I don't know any locals with either and its not right to torment a shopkeeper testing them out when I can afford neither (plus most shops around here won't simply order a £5K lens for you to test).