Both of these subs have new drivers that just came out within the past few months . . . therefore I don't think there has been a review that included both of these yet.
You might check out the reviews Ed has done in the past. Below is a link to a page with his reviews. He doesn't have the PB12 ISD/2, but did do the single driver version of both the Plus and the ISD. He also did the Plus/2.
My PB12-NSD/2 was just delivered yesterday. Unfortunately I am still waiting on delivery of some other components before I can set this thing up and give it a rip. I will report back as soon as I have it set up and give it a test drive.
And let me say this, nothing can prepare you for the shear size of this thing. You always hear and read in reviews "this sub is big!". Well, it is HUGE! It is a beast. So if you have a small space or the WAF won't allow for an end table sized sub, look out.