I have a decant of ARP, and I love it. However, I also own Black Aoud, Attar, and a decant of Aoud Queen Rose, and with slight variation they are all riffs on each other. BA might be a bit more "oud-y" than the rest, but only a real completeist, or a rose-crazy (like myself) should have all of the above.
If I had to come up with some distinction, I'd say that ARP has a bit more of a white, clear, tea rose top note to it. But that is me really digging for some difference.
Also, if it's any consolation to you, if I had to re-choose which of the Montale's that I own... I'd probably have chosen your Roses Petals over the Attar. So, good choice!