Just thought I'd close the loop on this thread. I ordered the Z5, but the bike shop was unable to get it from Felt b/c it was out of stock in my size when they went to order (several days later).

Amazingly, the LBS offered to sell me a Z4 for the SAME PRICE as the Z5, which was already on sale. Suffice it to say, I got a Ultegra equipped Z4 for $2K and couldn't be happier. It ended up taking a few extra weeks, but good things come to those who wait.

I've gotten three rides in so far and it's awesome. I'm knocking out neighborhood KOMs like candy and it's incredibly fun. The difference from a 27 lb. singlespeed hybrid-style bike to a 17 lb. Ultegra and carbon road bike is fairly pronounced, as you can imagine! Haha. I'm very glad to be back on a nice road bike after a couple of years rolling around on junky old bikes.