Adrian,
"Period" I guess it's a US thing, but it is an exagerration for emphasis that signifies there is nothing else to be said on the matter. The final word.I agree that the 15W1200 looks good, and it also has that great behavior in the crossover region like the Omega. As a midbass driver the smaller X-max is not much of an issue. According to box plot this thing will take more than its rated power without the voice coil ever leaving the gap, as long as you cross above 50Hz. Looks really good!
As far as 3dB down at 85Hz goes, your using that big sweaty sub with these aren't you. If so, Where are you crossing over? Besides room gain has usually started to kick in around 85 Hz. I think you could use either. That damn Omega is a charmer though. If you could get it for what we pay in the US, it would be a real winner. Is the price you listed for Omega 15 the price for one? If I've got my $AUD right thats almost double what we pay here. OUCH!
Anyway, I think you have it narrowed down to where you can't really do bad either way.
Later,
Thomas