Don't think that the Tamron has been put up against the
new 150-500 in any reviews, don't get confused with the old Sigma 170-500 that I had. Not doubting the Tamron is a super lens but unless any one has used both in the same conditions then an individual can not really comment on which is better. This is quite interesting
http://www.juzaphoto.com/eng/article...500_50-500.htm
and this is always a useful site
http://www.fredmiranda.com/reviews/
Hope they help.