Hmmm...well I hope I'm not ruining somebody's party here, but if you're up for them in yellow sapphire - the auction has started. I just fell over them looking for a yellow sapphire!
Yes I thought they were nicer too which is why I put them up. Diffusion. Hmmm...at first I thought nah! it would be like diffusing melee - do they? Then I thought, if they're baking a bunch of gravel before they cut it anyway, they may well throw in a teaspoon/cup/handful of beryllium.
If you look at the seller's store he/she has them in lots of different colours/stones. Pick one that's unlikely to be diffused OTOH I really rather liked the "multi-colored" sapphires which were different shades of grey and yellow - but not as well cut as you will see - so I think not?