New 5d3 or new lenses?

Hi there, I've got a 1d3, a 20d and come lenses like canon 17-55 2.8, 24-105, 135 f2, 50 1.4, 70-300 etc...

I do wedding photography and event photography... sometimes I feel that low light performances of my 1d3 could be a little better, so, do you think it's better for me to buy this new 5d3 and continue using my actual lenses or should I buy some lenses like 24-70 2.8 and/or 70-200 2.8?