The Ambrosio Nemesis is a pretty good old-school aluminum rim. About €90 I think. To that you propose adding a €320 titanium hub. I should say I have no direct experience with the Rocye hub, I just looked at its specs and price. And €320 is an extraordinary expense for a hub.

Keep in mind that in wheel design, it's optimal to reduce the weight of the wheel nearer the rim. Reducing weight near the hub is more like reducing non-rotating weight like frame and handlebars. I consider your plan to be spending way too much on the hub and not enough on the rim. Put another way: if its performance you are after spend more on the rims and perhaps consider carbon fiber, and save money on the hub. Or, get the Nemesis rims and save money on the hub - use a Campagnolo Record or Shimano Ultegra hub. Save yourself a few hundred Euro that probably isn't going to improve your ride experience that much.

I see a lot of positive comments on the Royce hub. It's ultralight and apparently well-liked in the weight-weinie community. But it apparently is also a bit hard to service (locknuts are, in my opinion, a horrible place to save weight with titanium), and the warranty is a bit difficult to get action on. And getting a freehub rebuilt by Royce is apparently very well done - but at £169 ($210) the cost to repair is more than the cost to buy most hubs!

I view the Royce hub as catering to a very narrow market of weight-wienies.

In sum:
If you have unlimited funds and want to build an ultra-prestigious and high-performance wheel, get the Royce hub and find lower weight rims.
Or, consider a Shimano Dura Ace hub which is also Ti, weighs less, and costs about the same amount.
If you want to spend money where it most matters, find better rims (or use the perfectly good Ambrosios) and get a more reasonably priced hub


This is what we say in English-speaking countries as "my 2 cents". That is my opinion.