used 16-35 or new 16-35 II?

Hi there, I'm going to buy the canon 16-35 to use with my 1d3 for weddings... I sent my 12-24 to repair and it's not coming back till september... so I'm without a wide lens and because I was planning to buy this lens from some months, now it's time.

I found the lens mark II at a local store for 1280€ (which is a good price here in Italy) and a lens mark I from a user of a forum for 800€.

So, which one to buy? mkII or mkI saving 480€?

my other equipment is:

canon 20D
canon 50 1.4
canon 135 f2
canon 70-300 is usm
canon 24-105
canon 430ex
metz 76

planning to buy 5d3 at the end of this wedding season and next buy will be a 70-200 2.8 (IS or not)