We came to a similar conclusion. Although we had already bought a diamond ring.

After researching, we figured out that we could sell our diamond (we only got about 60% of the original price back from a diamond broker) and buy a twice as large synthetic diamond and still save several thousand $.

There is only upside as far I can tell: it looks better (clarity), is bigger (no can tell the difference between a real and "fake" diamond), has fewer environmental and ethical externalities, and is cheaper.