Zipp 404 vs Shimano 7850-50

Hi, I am going to be buying a new carbon deep section wheelset for my bike and am stuck for choice between two wheelsets. I can get both of them for exactly the same price so that is not an issue. I am deciding between the Zipp 404 wheelset and the Shimano 7850-50 50mm wheelset, both in tubular. Do any of you have experiences with these wheels? The Zipps weigh in at 1250g a pair and the shimanos at 1469. What I would really like to know is if one wheelset is significantly more aero or stiffer. Most of the racing I do is on flat rolling courses. What wheelset would I be best to get?

There's some aero data here:
http://www.rouesartisanales.com/0-categorie-94458.html

Three of the 50mm-deep Shimanos tested about 3 watts less aero than some 2007 404s (for one wheel), which is obviously not much.

I've only had one very quick ride on some 404s, so I can't make a judgement. This might sound baseless, but I'd go for the 404s, just because they've proven themselves over a long time, and the 'word' at our races is that they're the 'fastest'. The consensus around here is that they are 'the schmiz'.

I've asked lots of guys if their (other) wheels are noticeably faster, and they usually say stuff like: "ah yeah, kinda", but the guys with Zipps usually say things like: "oh yeah, there are FAST"