First of all, the claimed weights are a lie. They are not 340g ea. The last pairs I saw on scales were 750 and 760 per pair, so you should figure that in your equation.
Second, how heavy are you and what kind of riding are you wanting to do on them?
Third is my reccomendation of velocity escapes. They are only 30g/pair heavier and I have been riding a pair for much of this year. They are tough (even good enough for 'cross). At 65-69kg I have had not broken a spoke in a year, the wheels are 3-4 years old (virtually no brake track left), built radially on the front, 28h front and rear, are plenty stiff and come in lots of pretty colours, if that is as important a motivation for you as it is me.
They also have a brake track, which is a nice thing.
If you want the lightest set of alloy tubs, you could try to hunt down a set of araya adx-1s. which are deeper than either of the above, a legit 335-345g, and stiff enough for me on a track bike. Damn near impossible to get outside of Japan though, it seems.
The ambrosios seem like a very nice rim. I have not built any up, but from all accounts they are very well made and somehow 'nicer' than anything else on the market. That said, they are not what you would call tough.