Is the old Canon 24-70 2.8 IS still better than the new Canon 24-70 2.8 IS Mark 2 ?

Hi guys I need your help! At the moment I am planning on buying the new Canon 24-70mm 2.8 lens however as i researched this lens i found out that it is not worth the extra £800.00 however most of the forum review didn't explain in depth why they think so. Have any of you done any research regarding this new Canon 24-70 2.8 lens ? if yes which one do you think I should go for ?

Thanks

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Lilyan Petrov
http://www.lilyan-petrov.co.uk