Is there a Zipp demo center in your area with a 808 front you can test? I think you will be surprised how easy a wheel the 808 is to ride, especially when you pair it with a disc. I would even consider a 1080. The crosswind performance difference between a 404 and 1080 is not all that high, especially since you rarely experience a true crosswind anyway. Think about the races you are currently doing, and the ones you want to do, is wind likely to be a problem? For most of us the answer is no. Sure it is windy sometimes at some races, but do you really want to make a wheel choice based on what might happen? As you mentioned, you have training wheels, so if you show up for the race and there is a 60mph crosswind use those.
Second, no matter what aero wheel you choose, get out and ride it. Train on it, especially on windy days, get used to riding an aero wheel in the wind. Get used to what happens when a semi passes you. People who have problems riding aero wheels typically have one thing in common…they only race on them. You wouldn’t do anything else on race day that you hadn’t tried first…don’t do it with your wheels. Carbon aero wheels are not as fragile as some think they are. Sure you hear about broken wheels, but no one gets online and posts about their ride “I rode my 404s today, they didn’t break, I will let you know how tomorrow goes.” There is a very low percentage of wheel returns compared to total sales, and a relatively small percentage of broken wheels in the pro peloton as well. Ride your race wheels, maybe not everyday, but at least once a week or so. I probably wouldn’t ride a disc this often, but I would train on it some, especially at first, until you became familiar with it.
Also, on the tubular vs clincher thing…don’t change a tubi during a race, use Vittorria PitStop. It may not work everytime, but it is by far the fastest option you have in case of a flat. If it doesn’t work, your race is probably over in anything shorter than a half anyway. Tubulars are lighter, and more aero. Rolling resistance can be debated, but fixing a flat is by far faster using the PitStop.
Whatever you chose, good luck with your race season. You can look up Zipp demo centers on www.zipp.com, go to dealers, demo centers have a yellow “D” logo beside them. Call and see if they have a 404, 808, or 1080, and try before you buy. If there isn’t one close, just know that whatever you chose is going to be fast. The speed differences between 404, 808, and 1080 are huge compared to a box section rim, but compared to each other, they are much closer.