Hi Robin…
Just wanted to add my .07 cents… I owned a pair of Zipps previously and I had problems with the hubs (three separate times, each time leaving me stranded). I realize/am aware they recently reworked their hubs, but my concern was more related to their customer service which I found to be somewhere between substandard and extremely poor. The first time they blamed the hub internals coming loose on user error (it came out while I was changing a flat). The second time they said it was the bike’s geometry putting stress on the hub that caused it to come loose (locking up my back wheel). The last time, they blamed it on the LBS failure to fix it right. There was no fourth time because they took the wheel back and supposedly sent it back to wherever they built them to rebuild the wheel itself. By that time, I purchased a set of Roval’s CL50’s (with DTS hubs) and haven’t looked back. No problems, easily serviced, with really good customer service. An example of the customer service is a friend of mine I race with was involved in a crash. Specialized replaced his wheel when the LBS couldn’t get it trued with no questions asked. That’s the customer service I should’ve gotten from Zipp.
Once you get past the price, what kind of customer support and service are you getting. That’s the question to ask. I hope this quick background helps in making your decision.