I would imagine that any 300G, 15k FC drive would be compatible with any other 300G, 15k FC drive (for example). But I don't know their support matrix on that, since each drive is given the microcode from the frame.
If you're looking at an XP, but aren't an AIX shop I would highly recommend looking at the rebranded SUN 9960 or HDS Lightning 9960 instead. The XP is highly tweeked for AIX and is really not considered the best of the three for non-AIX shops. But if you're looking at used and those aren't available used then I guess that kind of makes up your mind for you. ;-)
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"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
Albert Einstein