Sigma 500mm f/4 V Canon 500 f/4 mkii

I currently have the canon 500 f4 mk1 which is a great lens but I was planning on upgrading to the newer 500f4 mkii...
I have also been reading some reviews on the new Sigma 500f4 which seem to proclaim that it is a very sharp lens , I was wondering if anyone has tried the Sigma 500 and what were their views on it compared to the canon lenses. Also the Sigma is about £3000 cheaper than the canon lens here in the UK....Even if the Sigma was better than the canon 500mk1 it would seem like a good deal....
I would be interested to hear your thoughts..

I have, yet, to use the Sigma but it does look like a very good lens - but better than your 500 F4 L IS Mk1?

I have read around a little on this lens (I fancy a 500 Mk2 but can't afford it without selling the "Big Gun") and it does seem to be very good optically. However , whilst people report that the AF is very good I am not sure if it is up to my requirements - whereas the Canon 500 Mk1 or 2 is!

I am not saying that it won't do the job but, for me, I remain to be convinced - however I hope to try one as soon as possible! I am sure the Sigma is more than up to Airshows and the like, but I would like to try one out on birds in flight etc before deciding.

Just my thoughts............

There was a lot of noise a few months ago about the Sigma but I haven't seen too much talk about it since. Not sure why. That being said, the 500/4 II and its big brother the 600/4 II are two of the finest lenses ever made. Other than the cost, they really are flawless.

I agree they are the Kiddies! However, costing so much, we all look for affordable alternatives.

I can't help feeling that the OP is better off with their existing 500 Mk1 lens (I would certainly like one!) however the Mk2 is better, especially with extenders, but selling kidneys is a limited resource!

I think we will have to wait a while to get some real gen on the Sigma, I am sure it will be an excellent piece of kit, but to compete with the "Big Whites" is difficult - I wish then luck!