I'm looking to get a new set of wheels and have narrowed down to Zipp 303 or 404. My cycling route is mostly rolling terrain and flats but no hills. Which would offer the most performance advantage? My R3 weighs in at 7.76kg and I'm on a pair of Mavic Ksyrium SL '04 right now.

I have had many wheels sets under my SLC-SL and in my opinion the Zipps are a little mushy.  The Corima full carbon wheels are probably the best wheelset I've been on in terms of stiffness but the price is close to $4000.00.   The second best wheel I've had under my bike is the Reynolds DV46C.  It is a full carbon clincher with a 46mm depth.  The Zipp 404 has a 58mm depth and I found in the crosswinds of Texas, they really get pushed around.  The 46mm depth of the Reynolds handle it much better.  I also hit a crack in the road about a month ago that was about an inch wide and about 1 and 1/2 feet deep.  Needless to say, I went down (over the bars) and broke my front fork, but when I checked out the front wheel, it had no major damage.  It did get scratched some on the sides (a few lines) but it wasn't even out of true.  I think an aluminum rim probably would have folded up.  The weight on the DV46C is also under 1500 grams so they weight less than the Zipp wheelsets.  Check them out.  For the price, I don't think you can beat them.  Oh and by the way, they come with the Swiss DT240 hub.  WOW, what a smooth and fast hub!

Are you looking at clincher or tubular? I have ridden both 303 and 404 tubulars (currently run 303 tubulars). The new 404's are stronger with the new technology, etc. I probably wouldn't go Zipp if you are going clincher, in which case there are better clincher options out there (Rolf Vigor, etc.). Also, I think most would agree that carbon Zipps, and other carbon wheels, are really designed to be race wheels. I certainly wouldn't use my 303's for training (unless I win the lottery).

As for 303 vs. 404, I would agree with the above comment that in higher winds the 404's can get pushed around, but mostly what you would expect. I like the 303's for multi event use. The 404 are stiffer and feel a little quicker at top speed, the 303 are awesome on the hills. I think the best set-up is 303 front and 404 rear. Zipp also recommends it as a solid combo. Eliminates a lot of the crosswind issue, keeps it light, stiff in the rear, etc.

303's will likely drop over a pound off the bike fromm the SL's (if you go tubular).

I'm looking to go tubular. I'm just a weekend warrior and do not race at all. Also, a lot is going to boil down to cost. Over here in Singapore, a pair of 303s or 404s can be had for approx US$1650. That's a couple of hundred cheaper than the price over at CompetitveCyclist.com. I haven't checked out the price of Reynolds but the most likely candidate would be DV64T.

If you don't have any mountains around, you might as well go with 808's.  I have a pair of 404 tubulars for racing and they are exceptional on all terrain (from crits to mountain road races).

I race on the 404's and love them. i built them with DT Swiss hubs and cx-ray spokes.  i weigh 185 and they are stiff and fast... for just about any terrain i would go with the 404's.  look what 90% of the pros are riding: most are all on deeper section wheels, even in the hilly stages.   do your research, a fast set of wheels is not a light set of wheels [old school].   Wheel performance begins at 30mm+.   a 200g heavier wheel will only make a 30 meter difference on a  6 mile climb! 

Look at what Fabin, Voigt ride in almost all stages, 404's or bigger, even with hills.  Recardo Ricco [punk] even rode deep 50+ wheels in the up hill time trial in the Giro.  go to http://www.analyticcycling.com/  to get the exact analytic [unbiassed] stats. 

 I just went to 404's (dimpled clinchers) from SL's, and it is like riding a motorcycle at 20+ mph.  No problems in the wind.  My riding buddies could not believe the difference it made in my speed. Worth every penny if you are riding nothing bigger than rollers.

Not to confuse you, but I would suggest reconsidering Zipps as an everyday wheel... I don't race and I was looking for an everyday aero wheel to put on my R3 with a Powertap hub and was considering Zipp 404 clincher... Yet, when I started to research and discuss with dealers I was scared away from considering especially as many of my training roads can sometimes look a bit like Paris-Roubaix (well not quite)... I was scared off by the fear of damaging Zipps (I was considering clinchers)... So, in the end, I went with Bontrager Aeolus 5.0 and so far after 5000km on my rear wheel (with Powertap) I have had no issues and it remains true and intact... If I can get my boss, I plan to replace the front wheel with the matching Aeolus. Reviews have been wonderful as well. It is durable, comfortable, relatively light (for clincher).

Hey mtbnoob, where in Singapore can you get 404s for US$1650??? Cheapest I could ever find them was around the $US2000 - heading over there next month (from Australia) and pretty interested in replacing the Ksyriums

Thanks

Most of the authorized dealers for Zipp in Singapore would be able to match that price (about SGD2450). A point to note is that Zipp wheels in Singapore are built locally by Zipp's local dealer Robert Choy Imports. You can find this company on Zipp's website. The price does not include skewers though.

Having said that, my new pair of 303s are absolutely heavenly. No regrets even though I punctured on my 2nd outing with them.

I ride Zipp 404 clinchers on the R3 cos tubs are too much hassle. I have never had a problem with side winds and it can be pretty windy here in Scotland. The suggestion that 808's would be fine is ok if you never get a wind otherwise they are deadly and very scary. I have an 808 tub on the front of my TT bike but if it is windy I have to change it for a 404 tub. The combination of a disc and an 808 in the wind is not for the fainthearted. Buy the 404, you will not regret it they are an absolute joy and brilliant for climbing and descending.

Don