double refraction’s not something you can really see with the naked eye, you can only really see it with a loupe. The issue with the round brilliant cut is that it has a flatter crown and more needle like “arrows”, than the standard round brilliant. If you’re not too into cuts, you might not see the difference. It’ll have a glittery sparkle And will face up whiter, so in that sense it’s sparklier.
Oec’s will have larger more rainbowy flashes and show more body color. Personally I prefer the oec because I like the broad flashes, but it’s really a matter of taste.
*sigh* How I wish there were a store around me that carries moissanites so that I can see them in person! I can’t help but think that my visualizations probably aren’t like the real thing, and I wouldn’t want to buy two rings to compare. >.<
I own both an amora-ized OEC (7.5mm) and round brilliant stones, un-enhanced (5.5mm), and my RB stones show MUCH more body color than my OEC. I prefer the broader flashes of light returned with the OEC versus the splintery glitter effect seen with moissy RB stones, of course, once H&A cut moissy becomes available, I may change my mind and love them equally.
I’m pretty sure there are some videos on YouTube showing the difference between the cuts if you are interested.