Cab Pack Wizard
I actually own a couple of reference mics that I use for making sure my live room and control room work correctly. I've definitely done the tests with them but we talked about it with FAS and came to the conclusion that the whole neutral mic with mic simulations is kind of an old phase in IR evolution. Not to say that you can't get good tones with them because you definitely can and there are some appreciated FAS artists using those mic sims to get their sound but I aim for 100% authenticity and people aren't really using these mics with guitar cabinets in "real life".Bigger bang for the buck might be neutral reference mic captures like an Earthworks. Then we could use the mic sims and get the U87 and other flavors that way.
Do you know what's harder to find than a U87? A good U87 and a U87 that actually works. A producer friend of mine has bought a couple of vintage U87s and he said both of them were essentially not working properly which is normal. That being said it doesn't mean that they sound bad but I'd be super careful getting one of those and if I would have one.... let's just say that if you knew how loud my cabs are when I shoot IR's I wouldn't be too comfortable having that mic in the same room.